Patent Publication Number: US-6910228-B2

Title: Helmet

Description:
TECHNICAL FIELD 
   The present invention relates to a helmet which comprises a head protecting body to be worn on the head of a helmet wearer (to be merely referred to as a “wearer” hereinafter) such as the rider of a motor cycle to protect his/her head, and in which a ventilator mechanism for ventilation of the interior of the head protecting body and the like is provided to the head protecting body. 
   BACKGROUND ART 
   As a full-face-type helmet having a ventilator mechanism in its head protecting body for the purpose of ventilation of the interior of the head protecting body or fogging prevention of the inner surface of a shield plate, for example, one described in U.S. Pat. No. 5,093,938 is conventionally known. 
   The full-face-type helmet (to be merely referred to as “the conventional helmet” hereinafter). described in U.S. Pat. No. 5,093,938 has a forehead ventilator mechanism and chin ventilator mechanism above and under a window opening, which is formed in a full-face-type head protecting body to be worn on the head of the wearer, to oppose the face of the wearer. The forehead ventilator mechanism and chin ventilator mechanism have a forehead air supply hole and chin air supply hole, respectively. The forehead and chin air supply holes can be opened/closed by a forehead shutter member and chin shutter member, respectively. 
   Hence, in the conventional helmet, when the forehead air supply hole is opened, the outer air can be introduced into the head protecting body (i.e., the internal texture of the head protecting body itself and/or the head accommodating space of the head protecting body), to perform ventilation of the interior of the head protecting body. When the chin air supply hole is opened and the outer air is introduced into the head protecting body near the lower end of the inner surface of the shield plate, the introduced outer air moves up along the inner surface of the shield plate, to prevent fogging of the shield plate. 
   In the conventional helmet with the above arrangement, however, the outer air introduced into the head protecting body through the forehead air supply hole merely diffuses naturally over a wide range in the head protecting body, and draft for ventilation of the interior of the head protecting body and the like cannot be performed effectively. The outer air introduced into the head protecting body near the lower end of the inner surface of the shield plate through the chin air supply hole not only drifts upward along the inner surface of the shield plate, but its considerable portion naturally diffuses over a wide range in the head protecting body. Thus, fogging of the shield plate cannot be prevented well. 
   Therefore, with the conventional helmet, when it rains and the humidity is very high, ventilation of the interior of the head protecting body and fogging prevention of the shield plate cannot be performed effectively. 
   The present invention aims at effectively correcting the drawbacks of the conventional helmet described above with a comparatively simple arrangement. 
   DISCLOSURE OF INVENTION 
   According to the first aspect of the present invention, the present invention relates to a helmet comprising a head protecting body to be worn on a head of a helmet wearer, the head protecting body having a ventilator mechanism, wherein a stabilizer constituting member having a stabilizer portion is disposed on an outer side of the head protecting body, the stabilizer portion having an air current deflection surface which gradually separates from an outer surface of the head protecting body in a range of a front end to a rear end of the stabilizer portion, and a step surface extending from near the rear end of the air current deflection surface substantially toward the outer surface of the head protecting body, and a ventilation opening serving as an exhaust opening of the ventilation mechanism is formed in the step surface. 
   According to the second aspect of the present invention, the present invention relates to a helmet comprising a head protecting body to be worn on a head of a helmet wearer, the head protecting body having a ventilator mechanism, wherein a stabilizer constituting member commonly having a stabilizer portion and an air current divider portion provided independently of the stabilizer portion is disposed on an outer side of the head protecting body, the stabilizer portion having an air current deflection surface which gradually separates from an outer surface of the head protecting body in a range of a front end to a rear end of the stabilizer portion, and the air current divider portion having a substantially two-way forked projecting ridge such as a substantially V-shaped or substantially U-shaped projecting ridge, and a ventilation opening which is surrounded by the substantially two-way forked projecting ridge and serves as an exhaust opening of the ventilator mechanism. In the second aspect of the present invention, according to the first embodiment, the stabilizer portion further has a step surface extending from near a rear end of the air current deflection surface substantially toward the outer surface of the head protecting body, and a second ventilation opening serving as a second exhaust opening of the ventilation mechanism is formed in the step surface. 
   According to the third aspect of the present invention, the present invention relates to a helmet comprising a head protecting body to be worn on a head of a helmet wearer, the head protecting body having a ventilator mechanism, wherein a ventilation opening forming member commonly having a ventilation opening forming portion and an air current divider portion provided independently of the ventilation opening forming portion is disposed on an outer side of the head protecting body, the ventilation opening forming portion having an air current deflection surface which gradually separates from an outer surface of the head protecting body in a range of a front end to a rear end of the ventilation opening forming portion, and a step surface extending from near the rear end of the air current deflection surface substantially toward the outer surface of the head protecting body, and the air current divider portion having a substantially two-way forked projecting ridge such as a substantially V-shaped or substantially U-shaped projecting ridge, and a ventilation opening which is surrounded by the substantially two-way forked projecting ridge and serves as an exhaust opening of the ventilator mechanism, and a second ventilation opening serving as a second exhaust opening of the ventilator mechanism is formed in the step surface. 
   In the first embodiment of the second aspect of the present invention and the third aspect of the present invention, according to the second embodiment of the second aspect and the first embodiment of the third aspect, first and second ventilation openings may be formed in an outer shell of the head protecting body, and the helmet may further comprise at least one first exhaust path extending from the first ventilation opening of the outer shell to the ventilation opening of the air current divider portion, and at least one second exhaust path extending from the second ventilation opening of the outer shell to the second ventilation opening in the step surface, and a shutter mechanism which can commonly open and close at least one first exhaust path and at least one second exhaust path. In the second embodiment of the second aspect and the first embodiment of the third aspect of the present invention, according to the third embodiment of the second aspect and the second embodiment of the third aspect, the first exhaust path can comprise a pair of left and right first exhaust paths and the second exhaust path can comprise a pair of left and right second exhaust paths, and the shutter mechanism can commonly open and close the pair of left and right first exhaust paths and the pair of left and right second exhaust paths. Furthermore, in the first embodiment of the second aspect and the third aspect of the present invention, according to the fourth embodiment of the second aspect and the third embodiment of the third aspect, first and second ventilation openings may be formed in an outer shell of the head protecting body, and the helmet may further comprise a first exhaust path extending from the first ventilation opening of the outer shell to the second ventilation opening of the step surface, and a second exhaust path extending from the second ventilation opening of the outer shell to the ventilation opening of the air current divider portion, and no shutter mechanism that can open and close the first exhaust path, but a shutter mechanism that can open and close the second exhaust path. 
   According to the first aspect of the present invention, a ventilation opening serving as an exhaust opening of the ventilator mechanism is formed in the step surface of the stabilizer portion, and the step surface having the ventilator opening extends from near a rear end of the air current deflection surface substantially toward the outer surface of the head protecting body. Accordingly, the outer side of the exhaust opening is at a negative pressure, so that air in the head protecting body can be discharged well to the outside from the ventilation opening. Air in the head protecting body can be effectively discharged to the outside from the exhaust opening with a relatively simple structure. 
   According to the first and second aspects of the present invention, the traveling wind flowing along the outer surface of the head protecting body is forcibly separated from the outer surface of the head protecting body by the air current deflection surface of the stabilizer portion, and shifts relatively backward while it maintains a substantially laminar state. As the amount of traveling wind abruptly detouring to the rear portion of the head protecting body can be decreased, the drag and lift with respect to the head protecting body can be decreased. As a result, the traveling stability of the head protecting body can be achieved with a comparatively simple arrangement. 
   According to the second and third aspects of the present invention, the ventilation opening of the air current divider portion which serves as the exhaust opening of the ventilator mechanism is surrounded by the substantially two-way forked projecting ridge. Thus, the outer side of the ventilation opening is at a negative pressure, so that air in the head protecting body can be discharged well to the outside from the ventilation opening. 
   According to the first embodiment of the second aspect and the third aspect of the present invention, in addition to the ventilation opening of the air current divider portion which serves as the first exhaust opening of the ventilator mechanism, a second ventilation opening serving as a second exhaust opening of the ventilator mechanism is formed in the step surface of the stabilizer portion or ventilation opening forming portion, and the step surface having the ventilator opening extends from near a rear end of the air current deflection surface substantially toward the outer surface of the head protecting body. Accordingly, the outer side of the second exhaust opening is also at a negative pressure, so that air in the head protecting body can be discharged well to the outside from the second ventilation opening as well. Air in the head protecting body can be discharged to the outside more effectively from the two types of exhaust openings (i.e., first and second exhaust openings) with a relatively simple structure. 
   Furthermore, according to the second embodiment of the second aspect and the first embodiment of the third aspect of the present invention, the first exhaust path having the first exhaust opening as the terminal end and the second exhaust path having the second exhaust opening as the terminal end can be commonly opened and closed by a common shutter mechanism. Hence, these two types of exhaust paths (i.e., first and second exhaust paths) can be opened and closed easily. 
   According to the third embodiment of the second aspect and the second embodiment of the third aspect of the present invention, each of the first and second exhaust paths has a pair of left and right exhaust paths. Therefore, air in the head protecting body can be discharged to the outside more effectively. The pair of left and right first exhaust paths and the pair of left and right second exhaust paths can be commonly opened and closed by the common shutter mechanism. Therefore, these two types of exhaust paths, amounting to a total of four, can be opened and closed very easily. 
   According to the fourth embodiment of the second aspect and the third embodiment of the third aspect of the present invention, the arrangement and operation of the shutter mechanism can be simplified. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view, seen from obliquely behind the upper right, of the entire portion of a helmet according to the first embodiment in which the present invention is applied to a full-face-type helmet; 
       FIG. 2  is a right side view of the helmet of  FIG. 1 ; 
       FIG. 3  is a rear view of the helmet of  FIG. 1 ; 
       FIG. 4  is a front view of the helmet of  FIG. 1 ; 
       FIG. 5  is a perspective view, seen from obliquely behind the upper right, of a back head side ventilator mechanism of the helmet of  FIG. 1 , in which a ventilation opening forming member, serving also as a stabilizer constituting member, of the back head side ventilator mechanism is halved and one half is separated; 
       FIG. 6  is a partially cut-away perspective view, seen from obliquely behind the upper right, of the helmet of  FIG. 1 , in which various types of members attached to impact-on-the-head and impact-on-the-chin-and-cheek absorbing liners are omitted; 
       FIG. 7  is a partial enlarged view of  FIG. 6 ; 
       FIG. 8  is a perspective view, similar to  FIG. 6 , of the helmet of  FIG. 1  which is partially cut away at a position different from that of  FIG. 6 ; 
       FIG. 9  is a partial enlarged view of  FIG. 8 ; 
       FIG. 10  is an exploded perspective view of the impact-on-the-head and impact-on-the-chin-and-cheek absorbing liners of the helmet shown in  FIG. 1 ; 
       FIG. 11  is a perspective view, seen from obliquely behind the upper right, of the entire portion of a helmet according to the second embodiment in which the present invention is applied to a full-face-type helmet; 
       FIG. 12  is a right side view of the helmet of  FIG. 11 ; 
       FIG. 13  is a rear view of the helmet of  FIG. 11 ; 
       FIG. 14  is a front view of the helmet of  FIG. 11 ; 
       FIG. 15  is a perspective view, seen from obliquely behind the upper right, of a back head side ventilator mechanism of the helmet of  FIG. 11 , in which a ventilation opening forming member, serving also as a stabilizer constituting member, of the back head side ventilator mechanism is halved and one half is separated; 
       FIG. 16  is a plan view of the attaching member of the shutter mechanism shown in  FIG. 15 ; 
       FIG. 17  is a plan view of the shutter member of the shutter mechanism shown in  FIG. 15 ; 
       FIG. 18  is a longitudinal sectional view of the shutter mechanism shown in  FIG. 15  along an operating tap; and 
       FIG. 19  is a perspective view, seen from the left, of a back head side ventilator mechanism in the third embodiment in which the present invention is applied to a full-face-type helmet, where a ventilation opening forming member, serving also as a stabilizer constituting member, is indicated by an imaginary line. 
   

   BEST MODE OF CARRYING OUT THE INVENTION 
   The first, second and third embodiments in which the present invention is applied to a full-face-type helmet will be sequentially described separately with reference to the drawings. 
   1. First Embodiment 
   The first embodiment will be sequentially described separately into “entire helmet”, “impact-on-the-head and impact-on-the-chin-and-cheek absorbing liners”, “forehead and chin ventilator mechanisms” and “back head side ventilator mechanism” with reference to  FIGS. 1  to  10 . 
   (1) Entire Helmet 
   As shown in  FIGS. 1  to  4 , a full-face-type helmet  1  is made up of a full-face-type cap-like head protecting body  2  to be worn on the head of a wearer, a shield plate  4  capable of opening/closing a window opening  3  which is formed in the front surface of the head protecting body  2  to oppose that portion (i.e., the face) of the wearer, which is between the forehead and chin, and a pair of left and right chin straps (not shown in  FIGS. 1  to  4  as they are accommodated in the head protecting body  2  and can be conventional ones) attached to the inner side of the head protecting body  2 . A forehead ventilator mechanism  9  is formed at at least a part of the forehead region of the head protecting body  2 , which opposes the forehead of the wearer, and the vicinity of the forehead region. A chin ventilator mechanism  10  is formed at at least a part of the chin region of the head protecting body  2 , which opposes the chin of the wearer, and the vicinity of the chin region. A back head side ventilator mechanism  8  is formed at at least a part of the vertex region (i.e., its front and rear portions) and the upper portion of the occiput region of the head protecting body  2 , which correspond to the vertex part (i.e., its front and rear portions) and the upper portion of the occiput part of the head of the wearer, and their vicinities. In this specification, the front and rear portions of each of the vertex part of the head and the vertex region indicate the front and rear portions obtained when each of the vertex part of the head and the vertex region is halved into front and rear portions. The upper and lower portions of each of the occiput part of the head and the occiput region indicate the upper and lower portions obtained when each of the occiput part of the head and the occiput region is halved into upper and lower portions. 
   Hence, as shown in  FIGS. 6 and 8 , the head protecting body  2  can be made up of a full-face-type outer shell  5  which constitutes the outer circumferential wall of the head protecting body  2 , a lower rim member  6  having a substantially U-shaped cross-section and fixed to the outer shell  5  throughout the lower end of the outer shell  5  by adhesion or the like, a rim member  7  for a window opening, which has a substantially E-shaped cross-section and fixed to the outer shell  5  throughout the periphery of a window opening, formed in the outer shell  5  to form the window opening  3  of the head protecting body  2 , by adhesion or the like, a cap-like backing member  14  for the head, which is fixed to the outer shell  5  by adhesion or the like in contact with the inner surface of the outer shell  5  in a sinciput region, a vertex region, left and right temple regions and an occiput region respectively corresponding to the sinciput part, vertex part, left and right temple parts and occiput part of the head of the wearer, and a substantially semicircular ring-like backing member  15  for the chin and cheek, which is fixed to the outer shell  5  by adhesion or the like in contact with the inner surface of the outer shell  5  in chin and cheek regions respectively corresponding to the chin and cheeks of the wearer. The outer shell  5  can be made of a composite material formed by lining the inner surface of a strong shell body made of FRP or any other hard synthetic resin with a flexible sheet such as an unwoven fabric. The lower rim member  6  can be made of foamed vinyl chloride, synthetic rubber, or any other soft synthetic resin. The rim member  7  for the window opening can be made of an elastic material with high flexibility such as synthetic rubber. 
   As has been known, the backing member  14  for the head shown in  FIGS. 6 and 8  can be constituted by a cap-like impact-on-the-head absorbing liner  11  and a air-permeable backing cover for the head (not shown) attached to the impact-on-the-head absorbing liner  11  by adhesion, with a tape, or the like so as to cover almost the entire inner surface of the impact-on-the-head absorbing member  11  in the sinciput region, the vertex region and the occiput region excluding the left and right temple regions respectively corresponding to the left and right temple parts of the head of the wearer. As has been known, the backing member  15  for the chin and cheeks shown in  FIGS. 6 and 8  can be constituted by a substantially semicircular ring-like impact-on-the-chin-and-cheek absorbing liner  12  and a pair of left and right blockish inside pads (not shown) attached to the impact-on-the-chin-and-cheek absorbing liner  12  by adhesion or the like in contact with the inner surface of the impact-on-the-chin-and-cheek absorbing liner  12  by adhesion or the like in left and right cheek regions corresponding to the left and right cheeks of the wearer. 
   As has been known, the shield plate  4  is pivotally attached to the head protecting body  2  with a pair of right and left attaching screws  16 . The shield plate  4  closes the window opening  3  at the backward pivoting position shown in  FIGS. 2 and 4  and opens the window opening  3  at the forward pivoting position where the shield plate  4  has pivoted upward from the backward pivoting position. At the intermediate position between these positions, the shield plate  4  can partly open the window opening  3 . The shield plate  4  can be made of a transparent or translucent hard material such as polycarbonate or any other synthetic resin. In  FIGS. 2 and 4 , reference numeral  17  denotes a tap formed on the shield plate  4 . The tap  17  is held by the wearer with his fingers when the wearer is to pivot upward or downward the shield plate  4  forward or backward. Reference numeral  18  denotes an operating lever formed on the head protecting body  2 . The wearer operates the operating lever  18  when he is to operate the shield plate  4  to slightly pivot upward the shield plate  4 , located at the backward pivoting position, forward. 
   (2) Impact-On-The-Head and Impact-On-The-Chin-And-Cheek Absorbing Liners 
   As shown in  FIGS. 6 ,  8  and  10 , the impact-on-the-head absorbing liner  11  is constituted by a conventionally known impact-on-the-head absorbing liner having a sinciput region, a vertex region, left and right side temple regions and an occiput region, which is formed of a main liner member  22  having an outer recess  21  in its outer surface and an outer auxiliary liner member  23  attached to the main liner member  22  to fit with the outer recess  21 . The outer recess  21  extends from near a lower end  22   a  of the sinciput region of the main liner member  22  to the intermediate position of the occiput region or slightly above it through the sinciput region and vertex region, and has a substantially semicircular ring-like shape. A ventilation space  34 , which is narrower than the outer recess  21  and through which the outer recess  21  communicates with the lower end  22   a , is formed between the outer recess  21  and the lower end  22   a  of the sinciput region. The outer auxiliary liner member  23  has a substantially semicircular ring-like shape substantially identical with the outer recess  21 . The outer auxiliary liner member  23  is fitted in the outer recess  21  with its inner surface  23   a  in contact with a bottom surface  21   a  of the outer recess  21  of the main liner member  22 , so that it is attached to the main liner member  22 . The contact surfaces of the inner surface  23   a  and bottom surface  21   a  can be adhered with an adhesive or the like when necessary. 
   As shown in  FIGS. 6 ,  7  and  10 , the bottom surface  21   a  of the outer recess  21  of the main liner member  22  has a pair of left and right outer ridge grooves (i.e., laesulas)  24   a  and  24   b  which extend from the lower end  22   a  of the sinciput region to the intermediate position of the occiput region or slightly above it through the sinciput region and the vertex region (in other words, from the front end to rear end of the outer recess  21  throughout substantially its entire length). The terminal ends (i.e., rear ends) of the outer ridge grooves  24   a  and  24   b  connect to a pair of left and right through holes  25   a  and  25   b  which extend through the main liner member  22  substantially in the direction of thickness. The inner surface of the occiput region of the main liner member  22  (i.e., a surface on the side of the head accommodating space which accommodates the head of the wearer) has a pair of left and right inner ridge grooves (i.e., laesulas)  26   a  and  26   b  extending from the through holes  25   a  and  25   b  to a lower end  22   b  of the occiput region. The start ends (i.e., upper ends) of the inner ridge grooves  26   a  and  26   b  connect to the through holes  25   a  and  25   b.    
   As shown in  FIGS. 6 ,  7  and  10 , the inner surface  23   a  of the substantially semicircular ring-like outer auxiliary liner member  23  has a pair of left and right inner ridge grooves (i.e., laesulas)  27   a  and  27   b  so as to correspond to the pair of left and right outer ridge grooves  24   a  and  24   b  of the main liner member  22 . The inner ridge grooves  27   a  and  27   b  are formed throughout substantially the entire length in the back-and-forth direction of the outer auxiliary liner member  23 . When the outer auxiliary liner member  23  is attached to the main liner member  22  as described above, the inner ridge grooves  27   a  and  27   b  substantially overlap the outer ridge grooves  24   a  and  24   b  in the direction of thickness of the impact-on-the-head absorbing liner  11 , as shown in  FIGS. 6 and 7 . Hence, these ridge grooves  24   a  and  24   b , and  27   a  and  27   b  form a pair of left and right ventilation holes  28  inside the impact-on-the-head absorbing liner  11  (i.e., between the outer and inner surfaces). As shown in  FIGS. 6 and 7 , these ventilation holes  28  extend from a ventilation opening  34  to the through holes  25   a  and  25   b.    
   As shown in  FIGS. 6 ,  7  and  10 , the vertex region of the main liner member  22  has, at the vicinity of its rear end, a pair of left and right through holes  31   a  and  31   b  which connect to the pair of left and right outer ridge grooves  24   a  and  24   b  and extend through the main liner member  22  substantially in the direction of thickness. The outer auxiliary liner member  23  has a pair of left and right through holes  32   a  and  32   b , which extend through the outer auxiliary liner member  23  substantially in the direction of thickness, to respectively correspond to the pair of left and right through holes  31   a  and  31   b  of the main liner member  22 . When the outer auxiliary liner member  23  is attached to the main liner member  22  as described above, the through holes  32   a  and  32   b  overlap the through holes  31   a  and  31   b  in the direction of thickness of the impact-on-the-head absorbing liner  11  and communicate with them, as shown in  FIGS. 6 and 7 . Hence, these through holes  31   a  and  31   b , and  32   a  and  32   b  form the combinations of the pairs of left and right through holes  31   a  and  31   b , and  32   a  and  32   b  which extend through the impact-on-the-head absorbing liner  11  in substantially the direction of thickness. 
   An outer surface  23   b  of the outer auxiliary liner member  23  has a pair of left and right outer ridge grooves (i.e., laesulas)  29   a  and  29   b . The outer ridge grooves  29   a  and  29   b  extend from near the front end to a portion slightly behind the intermediate portion (in other words, near the intermediate position of the occiput region of the impact-on-the-head absorbing liner  11  or slightly above it) of the outer auxiliary liner member  23 . When the impact-on-the-head absorbing liner  11  is attached to the outer shell  5 , the outer surface  23   b  of the outer auxiliary liner member  23  is in contact with the inner surface of the outer shell  5 . Hence, the outer ridge grooves  29   a  and  29   b  and the inner surface of the outer shell  5  form a pair of left and right ventilation holes  30  in the outer surface of the impact-on-the-head absorbing liner  11 , as shown in  FIGS. 8 and 9 . These ventilation holes  30  extend from the ventilation space  34  to a portion slightly behind the intermediate portion of the outer auxiliary liner member  23 , as shown in  FIGS. 8 and 9 . 
   The pair of left and right ventilation holes  30  shown in  FIG. 9  (in other words, the pair of left and right outer ridge grooves  29   a  and  29   b ) are located between a pair of left and right ventilation holes  28  shown in  FIG. 8  (in other words, the pairs of the left and right ridge grooves  24   a  and  24   b , and  27   a  and  27   b ) in the left-to-right direction, as shown in FIG.  10 . Conversely to this, the pair of left and right ventilation holes  28  may be located between the pair of left and right ventilation holes  30  in the left-to-right direction. The pair of left and right ventilation holes  30  and the pair of left and right ventilation holes  28  can be arranged such that they are staggered in the left-to-right direction. 
   As described above, the inner surface of the impact-on-the-head absorbing liner  11  (in other words, the main liner member  22 ) is substantially covered by the backing cover for the head (not shown). Accordingly, the pair of left and right inner ridge grooves  26   a  and  26   b  formed in the inner surface of the main liner member  22 , and the backing cover for the head form a pair of left and right ventilation holes  33 , as shown in  FIGS. 6 and 10 . These ventilation holes  33  extend from the through holes  25   a  and  25   b  to the lower end of the impact-on-the-head absorbing liner  11 , as shown in FIG.  6 . As the backing cover for the head is air-permiable, these ventilation holes  33  are breathing with respect to the head accommodating space that accommodates the head of the wearer. 
   Of the substantially semicircular ring-like impact-on-the-chin-and-cheek absorbing liner  12 , its left and right ends in the horizontal direction are projected upward, so that a pair of left and right projections  12   a  and  12   b  are formed integrally with the liner  12 . When the impact-on-the-head absorbing liner  11  and impact-on-the-chin-and-cheek absorbing liner  12  are attached to the inner surface of the outer shell  5  in contact with it, the projections  12   a  and  12   b  abut against the lower surfaces of the left and right temple head regions of the impact-on-the-head absorbing liner  11 . 
   Each of the main liner member  22  and outer auxiliary liner member  23  of the impact-on-the-head absorbing liner  11  and of the impact-on-the-chin-and-cheek absorbing liner  12  can be made of a material with appropriate rigidity and plasticity such as polystyrene foam or any other synthetic resin. 
   (3) Forehead and Chin Ventilator Mechanisms 
   The forehead ventilator mechanism  9  shown in  FIGS. 2 ,  4  and  6  can be basically constituted by a ventilation opening forming member  42  attached to the forehead region on the outer surface of the outer shell  5  by adhesion or the like, and a shutter member  43  attached to the ventilation opening forming member  42  or outer shell  5  in order to open and close ventilation openings  44  formed in the ventilation opening forming member  42 , or a ventilation opening  37  formed in the outer shell  5 . When an operating tap  43   a  formed on the shutter member  43  is operated forward and backward, the shielding plate of the shutter member  43  opens and closes the ventilation openings  44  or ventilation opening  37 . 
   The chin ventilator mechanism  10  shown in  FIGS. 2 and 4  can be basically constituted by a ventilation opening forming member  46  attached to the chin region on the outer surface of the outer shell  5  by adhesion or the like, and a shutter member  47  attached to the ventilation opening forming member  46  or outer shell  5  in order to open and close ventilation openings  48  formed in the ventilation opening forming member  46 , or a ventilation opening (not shown) formed in the outer shell  5 . When an operating tap  47   a  formed on the shutter member  47  is operated forward and backward, the shielding plate of the shutter member  47  opens or closes the ventilation openings  48  or the ventilation opening of the outer shell  5 . 
   Hence, while the ventilation openings  44  of the forehead ventilator mechanism  9  and the ventilation openings  48  of the chin ventilator mechanism  10  respectively are open, when the wearer puts on the full-face-type helmet  1  and drives on a motor cycle, the forehead ventilator mechanism  9  and chin ventilator mechanism  10  function in the following manner. 
   More specifically, the outer air relatively flowing from the ventilation openings (i.e., intake openings)  48  of the chin ventilator mechanism  10  to the inside of the ventilation opening forming member  46  flows relatively into a ventilation space (not shown), formed between the outer shell  5  and impact-on-the-chin-and-cheek absorbing liner  12 , through the ventilation opening (i.e., intake opening) formed in the outer shell  5 . The outer air then rises from the ventilation space to near the lower end of the inner surface of the shield plate  4 . At least part of the outer air that has risen further rises from near the lower end to near the upper end of the inner surface of the shield plate  4  along the inner surface of the shield plate  4 . Therefore, the outer air effectively prevents the shield plate  4  from being fogged by the breath exhaled by the wearer. 
   At least part of the outer air that has risen near the upper end of the inner surface of the shield plate  4  flows into the ventilation space  34  through a ventilation opening  36  formed in a locking member  35  attached to the lower end portion of the sinciput region (i.e., the lower end portion of the forehead region) of the main liner member  22 , as shown in  FIGS. 6  to  9 . As has been known, the locking member  35  is used for attaching a backing cover for the head (not shown) to the impact-on-the-head absorbing liner  11 . 
   The outer air that has relatively flown from the ventilation openings (i.e., intake openings)  44  of the forehead ventilator mechanism  9  to the inside of the ventilation opening forming member  42  relatively flows into the ventilation space  34  through the ventilation opening (i.e., intake opening)  37  formed in the outer shell  5 . Part of each of the two types of outer air that has flown from the ventilation openings  36  and  37  into the ventilation space  34  flows into the ventilation holes  28  and shifts backward in the impact-on-the-head absorbing liner  11 , while another part flows into the ventilation holes  30  and shifts backward along the outer surface of the impact-on-the-head absorbing liner  11  (in other words, the outer auxiliary liner member  23 ). 
   In place of the forehead ventilator mechanism  9 , or in addition to the forehead ventilator mechanism  9  as shown in the second embodiment (to be described later), a front head side ventilator mechanism (not shown) having an arrangement identical to that of the forehead ventilator mechanism  9  can be formed at at least part of the upper portion of the sinciput region and the front portion of the vertex region on the outer surface of the outer shell  5  and their vicinities. In this specification, the upper portion of each of the sinciput part of the head and the sinciput region indicates the upper portion which is obtained when each of the sinciput part of the head and the sinciput region is halved. 
   Each of the ventilation opening forming members  42  and  46  and of the shutter members  43  and  47  can be made of a material with appropriate elasticity and rigidity such as polycarbonate, polyacetal, ABS, nylon, or any other synthetic resin. 
   (4) Back Head Side Ventilator Mechanism 
   The back head side ventilator mechanism  8  shown in  FIGS. 1  to  3  and  FIGS. 5  to  9  can be basically constituted by a ventilation opening forming member  51  serving also as a stabilizer constituting member, and a pair of left and right shutter mechanisms  56  attached to the outer shell  5  or ventilation opening forming member  51 . The pair of left and right shutter mechanisms  56  are formed to open and close a pair of left and right ventilation openings  52   a  and  52   b  and a pair of left and right ventilation openings  53   a  and  53   b  formed in the outer shell  5 , or open and close a pair of left and right ventilation openings  54   a  and  54   b  formed in the ventilation opening forming member  51 , and a series of ventilation openings  55   a ,  55   b  and  55   c  extending in the left-to-right direction. The shutter mechanisms  56  have a pair of left and right operating taps  57   a  and  57   b . When the operating taps  57   a  and  57   b  are operated forward and backward, the shielding plates (to be described later) of the shutter mechanisms  56  open and close the ventilation openings  52   a  and  53   a , and  52   b  and  53   b , or open and close the ventilation openings  54   a  and  54   b , and  55   a  to  55   c.    
   The practical structures of the ventilation opening forming member  51  and shutter mechanisms  56  will be described with reference to FIG.  1  and  FIGS. 5  to  9 . 
   As shown in  FIGS. 6  to  9 , the ventilation opening forming member  51  can be attached to the outer surface of the outer shell  5  at at least part of the vertex region (i.e., its front and rear portions) and the upper portion of the occiput region of the outer shell  5 , and their vicinities. In the embodiment shown in  FIGS. 6  to  9 , the ventilation opening forming member  51  is attached at substantially the central position in the left-to-right direction. The ventilation opening forming member  51  serves also as the stabilizer constituting member. As shown in  FIGS. 1 and 3  and  FIGS. 5  to  7 , the ventilation opening forming member  51  has a stabilizer portion  61  serving also as a ventilation opening forming portion at substantially its central portion in the left-to-right direction, and a left air current divider portion  62   a  and right air current divider portion  62   b  which are adjacent to the left and right sides of the stabilizer portion  61 . Hence, the stabilizer portion  61  serving also as the ventilation opening forming portion and the pair of left and right air current divider portions  62   a  and  62   b  are formed in common at the integrally molded single ventilation opening forming member  51 . 
   As shown in  FIG. 5 , the stabilizer  61  has an air current deflection portion or air current deflection surface  63  extending backward from near the boundary of the vertex region and occiput region of the outer surface of the outer shell  5 , and a step portion or step surface  64  formed by bending the air current deflection surface  63  at its lower end (i.e., rear end) substantially toward the outer surface of the outer shell  5 . The outer surface of the air current deflection surface  63  at the front end is substantially flush with the outer surface of the outer shell  5 . In order to form this arrangement easily, a recess  74  may be formed in that outer side surface of the outer shell  5  which corresponds to the ventilation opening forming member  51 , as shown in  FIGS. 7 and 9 . The air current deflection surface  63  gradually separates from the outer surface of the outer shell  5  in the range of the front end to the rear end, and is the farthest at its rear end from the outer side surface of the outer shell  5 . The step surface  64  extends from the rear end of the air current deflection surface  63  substantially toward the outer surface of the outer shell  5  till near its outer surface, and extends long substantially like a band in the left-to-right direction. One or a plurality of ventilation openings  55   a ,  55   b  and  55   c  are formed in the step surface  64 . In the embodiment shown in FIG.  1  and  FIGS. 5  to  9 , the number of ventilation openings is three. The three ventilation openings  55   a ,  55   b  and  55   c  extending horizontally in the left-to-right direction are formed in a row in the left-to-right direction. 
   An average angle formed by the air current deflection surface  63  and step surface  64  is about 75° in the embodiment shown in FIG.  1  and  FIGS. 5  to  9 , but generally preferably falls within a range of 45° to 120° from the viewpoint of practicality, and more preferably a range of 60° to 100°. The air current deflection surface  63  can be substantially rectangular, and its average length L 1  (see  FIG. 3 ) in the left-to-right direction (a length between the left and right ends actually along the air current deflection surface  63 ) is about 120 mm in the embodiment shown in  FIG. 3 , but generally preferably falls within a range of 60 mm to 240 mm from the viewpoint of practicality, and more preferably a range of 80 mm to 180 mm. An average length L 2  (see  FIG. 6 ) in the back-and-forth direction (a length between the front and rear ends actually along the air current deflection surface  63 ) of the air current deflection surface  63  is about 60 mm in the embodiment shown in  FIG. 6 , but generally preferably falls within a range of 30 mm to 120 mm from the viewpoint of practicality, and more preferably a range of 40 mm to 90 mm. An average length (i.e., width) L 3  (see  FIG. 3 ) of the step surface  64  (but at its portion which opposes the air current deflection surface  63  in the back-and-forth direction) in a direction substantially perpendicular to the left-to-right direction is about 10 mm in the embodiment shown in  FIG. 3 , but generally preferably falls within a range of 4 mm to 26 mm from the viewpoint of practicality, and more preferably a range of 6 mm to 18 mm. 
   The pair of left and right air current divider portions  62   a  and  62   b  can be axi-symmetric to each other with respect to a center line (actually a center plane)  75  (see  FIG. 3 ) of the full-face-type helmet  1  which extends in the back-and-forth direction. Hence, in the following description, the right air current divider portion  62   b  will be described in detail, and a detailed description on the left air current divider portion  62   a  will be omitted. 
   As shown in  FIG. 5 , the air current divider portion  62   b  has a pair of left and right projecting ridges  65   a  and  65   b  extending substantially in the back-and-forth direction. The projecting ridges  65   a  and  65   b  are continuous to each other at their front ends, and their rear ends extend to gradually open apart substantially backward, to form a substantially V-shaped or two-way forked projecting portion  66  as a whole. In the specification, that projecting ridge which is located nearer the center line  75  is denoted by reference numeral  65   a , and that projecting ridge which is located on the opposite side of the center line  75  (i.e., on the outer side in the left-to-right direction) is denoted by reference numeral  65   b.    
   The air current divider portion  62   b  has a substantially acute triangular bottom surface  67  formed of a region surrounded by the V-shaped or two-way forked projecting ridge  66 , as shown in FIG.  5 . The ventilation opening  54   b  ( 54   a  in the case of the left air current divider portion  62   a ) is formed near the front end of the bottom surface  67 , and an operating tap slit  60  is formed at substantially the central portion of the bottom surface  67 . Although only one ventilation opening  54   b  is formed in each bottom surface  67  in the embodiment shown in  FIG. 5 , a plurality of ventilation openings  54   b  may be formed. Hence, the ventilation opening  54   b  is surrounded by that portion of the V-shaped projecting ridge  66  which is near its front end. The V-shaped projecting ridge  66  and the bottom surface  67  are continuous to each other through a substantially V-shaped or two-way forked step portion or step surface  69 . An outer peripheral portion (i.e., a V-shaped peripheral portion)  68  of the V-shaped projecting ridge  66  which is on the opposite side to the V-shaped step surface  69  gradually separates from the outer surface of the outer shell  5  in the range of the outer surface of the outer shell  5  to the V-shaped step surface  69 , and is the farthest at its portion which is adjacent to the V-shaped step surface  69 . 
   One half (i.e., one step surface portion)  69   a  of the V-shaped or two-way forked step surface  69  which is adjacent to the projecting ridge  65   a  at the center side in the left-to-right direction can be inclined from the outer side to the inner side at an appropriate angle with respect to the center line  75  in the range of the front end to the rear end. An average angle of inclination is about 15° in the embodiment shown in  FIG. 5 , but generally preferably falls within a range of −10° to 40° from the viewpoint of practicality, and more preferably a range of 5° to 25°. The other half (i.e., the other step surface portion)  69   b  of the V-shaped or two-way forked step surface  69  which is adjacent to the outer projecting ridge  65   b  in the left-to-right direction can be inclined from the inner side to the outer side at an appropriate angle with respect to the center line  75  in the range of the front end to the rear end. An average angle of inclination is about 20° in the embodiment shown in  FIG. 5 , but generally preferably falls within a range of −5° to 45° from the viewpoint of practicality, and more preferably a range of 10° to 30°. Hence, an average angle formed by the pair of step surface portions  69   a  and  69   b  of the V-shaped or two-way forked step surface  69  is about 35° in the embodiment shown in  FIG. 5 , but generally preferably falls within a range of 15° to 60° from the viewpoint of practicality, and more preferably a range of 20° to 50°. 
   A linear length (i.e., linear width) L 4  (see  FIG. 5 ) of the V-shaped or two-way forked step surface  69  from the bottom surface  67  to the V-shaped projecting ridge  66  is about 6.5 mm around the ventilation opening  54   b  ( 54   a  in the case of the left air current divider portion  62   a ) in the embodiment shown in  FIG. 5 , but generally preferably falls within a range of 2.5 mm to 16 mm from the viewpoint of practicality, and more preferably a range of 4.5 mm to 12 mm. 
   The portion between that end (i.e., the proximal end) of the V-shaped step surface  69  which is near the bottom surface  67  and that end (i.e., the distal end) which is near the V-shaped projecting ridge  66  need not be linear, but may form, e.g., a recessed surface toward the V-shaped projecting ridge  66 . The width L 4  of the V-shaped step surface  69  can gradually decrease from the front ends to the rear ends of the projecting ridges  65   a  and  65   b , and can be equal to ¼ or less the maximum value of the above width, or substantially zero at the rear ends of the projecting ridges  65   a  and  65   b.    
   The lengths (lengths actually along the step surface  69 ) of one half  69   a  and the other half  69   b  of the V-shaped or two-way forked step surface  69  are respectively about 80 mm and about 90 mm in the embodiment shown in  FIG. 5 , but generally preferably fall within a range of 30 mm to 200 mm from the viewpoint of practicality, and more preferably a range of 40 mm to 160 mm. A distance (a length actually along the bottom surface  67 ) L 5  (see  FIG. 5 ) between the rear end of one half  69   a  and the rear end of the other half  69   b  of the V-shaped step surface  69  is about 60 mm in the embodiment shown in  FIG. 5 , but generally preferably falls within a range of 30 mm to 120 mm from the viewpoint of practicality, and more preferably a range of 40 mm to 90 mm. An average angle of inclination (particularly an average angle around the ventilation opening  54   b ) formed by the V-shaped step surface  69  with respect to the outer surface (that portion opposing the v-shaped projecting ridge  66 ) of the outer shell  5  is about 60° in the embodiment shown in  FIG. 5 , but generally preferably falls within a range of 35° to 120° from the viewpoint of practicality, and more preferably a range of 45° to 100°. 
   The rear ends of the bottom surfaces  67  of the air current divider portions  62   a  and  62   b  continue to the step surface  64  of the stabilizer portion  61 . The width of the step surface  64  gradually decreases at the continuous portion toward the two outer sides in the left-to-right direction. A connecting portion  70  extending like a band in the left-to-right direction substantially along the outer surface of the outer shell  5  is integrally formed at the rear end of the step surface  64 . Hence, in the ventilation opening forming member  51 , the stabilizer portion  61 , pair of left and right air current divider portions  62   a  and  62   b  and connected portion  70  are molded integrally. 
   The pair of left and right shutter mechanisms  56  can be axi-symmetric to each other with respect to the center line  75  as the axis of symmetry. Accordingly, in the following description, the right shutter mechanism  56  will be described in detail, and a detailed description on the left shutter mechanism  56  will be omitted. 
   The right shutter mechanism  56  has a main shutter member  81  serving also as an operating member, and an auxiliary shutter member  82 . The right shutter mechanisms  56 , except for the operating tap  57   b  ( 57   a  in the case of the left shutter mechanism  56 ) formed on the main shutter member  81 , is covered with the ventilation opening forming member  51 , the inner periphery of which is attached to the outer surface of the outer shell  5  by adhesion with an adhesive or the like. Therefore, the ventilation opening forming member  51  also serves as a cover member for the pair of left and right shutter mechanisms  56 . 
   As shown in  FIGS. 8 and 9 , a ventilation space  71  is formed between the ventilation opening forming member  51  and outer shell  5 . The pair of left and right ventilation openings  53   a  and  53   b  formed in the outer shell  5  are continuous to the terminal ends (i.e., rear ends) of the pair of left and right ventilation holes  30  formed between the outer surface  23   b  of the outer auxiliary liner member  23  (in other words, the impact-on-the-head absorbing liner  11 ) and the inner surface of the outer shell  5 . Therefore, a first exhaust path  72  constituted by the ventilation openings  53   a  and  53   b →ventilation space  71 →ventilation openings  55   a ,  55   b  and  55   c  is formed in the head protecting body  2 . 
   As shown in  FIGS. 6 and 7 , the pair of left and right ventilation openings  52   a  and  52   b  formed in the outer shell  5  are respectively continuous to the pair of left and right through holes  32   a  and  32   b  formed in the outer auxiliary liner member  23  (in other words, the impact-on-the-head absorbing liner  11 ). The pair of left and right ventilation openings  54   a  and  54   b  formed in the ventilation opening forming member  51  are respectively continuous to the pair of left and right ventilation openings  52   a  and  52   b  and the pair of left and right through holes  32   a  and  32   b . Therefore, a pair of left and right second exhaust paths  73  constituted by the pair of left and right ventilation openings  52   a  and  52   b →ventilation space  71 →pair of left and right ventilation openings  54   a  and  54   b  are formed in the head protecting body  2 . The pair of left and right ventilation openings  54   a  and  54   b  can set to oppose the pair of left and right ventilation openings  52   a  and  52   b  while they are away from them by a distance substantially corresponding to the thickness of the main shutter member  81 . 
   As shown in  FIG. 5 , the main shutter member  81  can be a longitudinal plate body extending substantially along the longitudinal direction of the outer projecting ridge  65   b  of the V-shaped projecting ridge  66 . The main shutter member  81  has a pair of front and rear guide slits  83  and  84  extending substantially along its longitudinal direction. One side edge of the front slit  83  forms an elastic deformable portion  85  which is curved in the lateral direction toward the front slit  83 . Hence, the front slit  83  has a function of holding a guide projection  86  (to be described later) in position. The main shutter member  81  also integrally has the operating tap  57   b  ( 57   a  in the case of the left shutter mechanism  56 ) which can be operated forward and backward substantially along its longitudinal direction. 
   The outer shell  5  has the upper guide projection  86  and a lower guide projection  87 , which form a pair and oppose the pair of upper and lower slits  83  and  84 . The projections  86  and  87  are inserted in the guide slits  83  and  84  to be slidable relative to them. Near one end of the main shutter member  81 , the auxiliary shutter member  82  is pivotally, axially supported, at its portion near its one end, by a shaft  88 . The auxiliary shutter member  82  can be a longitudinal plate body extending substantially perpendicularly to the center line  75 . 
   The outer shell  5  has a pair of front and rear support rods  89  and  90  for supporting the auxiliary shutter member  82 , such that they oppose the intermediate portion of the auxiliary shutter member  82 . The support rods  89  and  90  oppose each other at a distance substantially corresponding to the width of the intermediate portion of the auxiliary shutter member  82 . The opposing surfaces of the support rods  89  and  90  form substantially semicircular cylindrical convex surfaces. The guide projections  86  and  87  and the support rods  89  and  90  need not be directly formed on the outer shell  5 . All or some of the guide projections  86  and  87  and support rods  89  and  90  may be formed on a common auxiliary plate, and after that the auxiliary plate may be attached to the outer surface of the outer shell  5  by adhesion with, e.g., an adhesive. 
   A shielding plate  81   a  is formed at the free end of the main shutter member  81  to correspond to the ventilation opening  52   b  of the outer shell  5 . Another shielding plate portion  82   a  is formed at the free end of the auxiliary shutter member  82  to correspond to the ventilation opening  53   b  of the outer shell  5 . 
   Therefore, as shown in  FIG. 5 , while the ventilation openings  52   b  and  53   b  of the outer shell  5  is open, when the operating tap  57   b  ( 57   a  in the case of the left shutter mechanism  56 ) exposed to the outside through the operating tap slit  60  of the ventilation opening forming member  51  is operated forward, the main shutter member  81  moves forward toward the front side due to the guide function for the linear reciprocal motion of the guide slits  83  and  84  and guide projections  86  and  87 . Hence, the shielding plate portion  81   a  of the main shutter member  81  closes the ventilation opening  52   b  ( 52   a  in the case of the left shutter mechanism  56 ) of the outer shell  5  from the outer surface. In this case, the shielding plate portion  81   a  may simultaneously close the ventilation opening  54   b  ( 54   a  in the case of the left shutter mechanism  56 ) of the ventilation opening forming member  51 . Thus, the ventilation opening  52   b  changes from the open state to the closed state. When the main shutter member  81  is moved forward, the auxiliary shutter member  82  pivots forward clockwise in  FIG. 5  about its intermediate portion as a fulcrum. Accordingly, the shielding plate portion  82   a  of the auxiliary shutter member  82  closes the ventilation opening  53   b  ( 53   a  in the case of the left shutter mechanism  56 ) of the outer shell  5  from the outer surface. Thus, the ventilation opening  53   b  changes from the open state to the closed state. 
   As described above, the ventilation openings  52   b  and  53   b  are closed or opened simultaneously upon the forward/backward operation of the single operating tap  57   b . The right half of each of the first and second exhaust paths  72  and  73  can be closed or opened simultaneously. Upon the forward/backward operation, the guide projection  86  moves relatively to and fro in the guide slit  83  while temporarily elastically deforming the elastic deformable portion  85 . Hence, the guide projection  86  will not accidentally move in the guide slit  83  relatively to and fro. Whether the operating tap  57   b  is operated forward or backward, the operating tap slit  60  is closed by the main shutter member  81 . 
   In place of the elastic deformable portion  85 , or in addition to the elastic deformable portion  85 , a groove extending substantially along the direction of the reciprocal motion of the main shutter member  81  may be formed in the guide projection  86 , so that elasticity can be imparted to the guide projection  86  itself. Each constituent member of the ventilation opening forming member  51  and shutter mechanisms  56  can be made of a material with appropriate elasticity and rigidity such as polycarbonate, polyacetal, ABS, nylon, or any other synthetic resin. 
   While the ventilation openings  52   a ,  52   b ,  53   a  and  53   b  of the back head side ventilator mechanism  8  having the above arrangement are open, when the wearer puts on the full-face-type helmet  1  and drives on a motor cycle, the back head side ventilator mechanism  8  operates in the following manner. 
   The traveling wind (i.e., outer air) flowing substantially along the outer surface of the outer shell  5  is relatively directed toward the occiput region through the vertex region. Thus, the traveling wind is forcibly separated from the outer surface of the outer shell  5  by the air current deflection surface  63  of the stabilizer portion  61 , and shifts relatively backward while it maintains a substantially laminar state. As the amount of traveling wind abruptly detouring to the lower portion of the occiput region of the outer shell  5  is small, the drag (backward force) and lift (floating force) with respect to the head protecting body  2  can be decreased. As a negative pressure is generated near the step surface  64  of the stabilizer portion  61 , air in the ventilation space  71  is forcibly discharged to the outside from the ventilation openings  55   a ,  55   b  and  55   c  serving as exhaust openings. 
   As the traveling wind is also directed relatively toward the V-shaped projecting ridges  66  of the air current divider portions  62   a  and  62   b , it shifts relatively backward while it is divided into the left and right by the respective V-shaped projecting ridges  66 . Hence, a negative pressure is generated near the V-shaped step surfaces  69  and bottom surfaces  67  of the air current divider portions  62   a  and  62   b , and accordingly air in the ventilation space  71  is forcibly discharged to the outside from the ventilation openings  54   a  and  54   b  serving as exhaust openings. The substantially V-shaped projecting ridge  66  extending substantially in the back-and-forth direction and the substantially V-shaped step surface  69  extending substantially in the back-and-forth direction are axi-symmetrical. Thus, the pair of left and right air current divider portions  62   a  and  62   b  can prevent to a certain degree the wobbling of the head protecting body  2  in the left-to-right direction caused by the traveling wind. Also, the drag and lift can be decreased, if a little, because of substantially the same reason as in the case of the stabilizer portion  61 . 
   As described in item (3) (item of “Forehead and Chin Ventilator Mechanisms”), air that has flown into the pair of left and right ventilation holes  28  and shifted to the pair of left and right through holes  32   a  and  32   b  of the outer auxiliary liner member  23  mixes with air that has shifted from the head accommodating space of the head protecting body  2  to the through holes  32   a  and  32   b  through the pair of left and right through holes  31   a  and  31   b  of the main liner member  22 , as is apparent from  FIGS. 6 and 7 . Part of the air mixture is discharged well to the outside, which is set at the negative pressure as described above, from the ventilation openings  54   a  and  54   b  through the pair of left and right second exhaust paths  73  described above. Another part of the air mixture shifts further downward through the pair of left and right ventilation holes  28  and is discharged to the outside from the lower end portion of the occiput region of the head protecting body  2  through the pair of left and right through holes  25   a  and  25   b  and the pair of left and right ventilation holes  33 , as is apparent from  FIGS. 6 and 7 . 
   As is described in item (3), air that has flown into the pair of left and right ventilation holes  30  and shifted to their terminal ends is discharged well to the outside, which is at the negative pressure as described above, from the ventilation openings  55   a ,  55   b  and  55   c  through the first exhaust path  72  described above, as is apparent from  FIGS. 8 and 9 . 
   2. Second Embodiment 
   The second embodiment will be described with reference to  FIGS. 11  to  18 . The second embodiment can be substantially the same as the first embodiment described above except that 
   (1) a front head side ventilator mechanism  91  is newly added, 
   (2) the practical structure of shutter mechanisms  56  of a back head side ventilator mechanism  8  is different, 
   (3) the practical shape of a ventilation opening forming member  51  serving also as a stabilizer constituting member is slightly different, 
   (4) a pair of left and right ventilation openings  92   a  and  92   b  are newly formed in the lower portion of the occiput region of an outer shell  5 , and 
   (5) the arrangements of ventilation openings and ridge grooves formed in the outer shell  5  and in an impact-on-the-head absorbing liner  11  are slightly different. Hence, in the following description, only these differences will be described separately, and a description on portions that are common to the first and second embodiments will be omitted. 
   (1) Front Head Side Ventilator Mechanism 
   As shown in  FIGS. 12 and 14 , the front head side ventilator mechanism  91  is formed at at least part of the upper portion of the sinciput region and the front portion of the vertex region of a head protecting body  2 , which respectively correspond to the upper portion of the sinciput part and the front portion of the vertex part of the head of the wearer, and their vicinities. The front head side ventilator mechanism  91  is located at the intermediate portion between a forehead ventilator mechanism  9  and the back head side back head side ventilator mechanism  8  in the back-and-forth direction. 
   The front head side ventilator mechanism  91  shown in  FIGS. 12 and 14  can be basically constituted by a ventilation opening forming member  93  attached to a predetermined region (i.e., at least part of the upper portion of the sinciput region, the front portion of the vertex region and their vicinities) on the outer surface of the outer shell  5  by adhesion or the like, and a shutter member  95  attached to the ventilation opening forming member  93  or outer shell  5  in order to open and close a ventilation opening  94  formed in the ventilation opening forming member  93  or a ventilation opening (not shown) formed in the outer shell  5 . When an operating tap  95   a  formed on the shutter member  95  is operated forward and backward, the shielding plate portion of the shutter member  95  opens and closes the ventilation opening  94  or the ventilation opening of the outer shell  5 . 
   The ventilation opening of the outer shell  5  can consist of a pair of left and right ventilation openings. The pair of left and right ventilation openings can communicate with a pair of left and right through holes (not shown) extending to the head accommodating space of the impact-on-the-head absorbing liner  11  through the impact-on-the-head absorbing liner  11  (i.e., an outer auxiliary liner member  23  and main liner member  22 ). The pair of left and right ventilation openings and the pair of left and right through holes need not communicate with ventilation holes  28  and  30  but can be independent of them. The shutter member  95  can be attached to the outer shell  5  through a shutter attaching member (not shown). In this case, the shutter attaching member can be attached to the outer surface of the outer shell  5  by adhesion or the like, and the shutter member  95  can be attached to the shutter attaching member to be substantially movable forward and backward in the left-to-right direction. 
   Therefore, while the shutter member  95  of the front head side ventilator mechanism  91  is open and the ventilation opening  94  communicates with the head accommodating space of the impact-on-the-head absorbing liner  11 , when the wearer puts on a full-face-type helmet  1  and drives on a motor cycle, the front head side ventilator mechanism  91  operates in the following manner. 
   More specifically, outer air that has flown relatively to the inside of the ventilation opening forming member  93  from the ventilation opening (i.e., intake opening)  94  of the front head side ventilator mechanism  91  flows relatively into the head accommodating space of the impact-on-the-head absorbing liner  11  from the pair of left and right ventilation openings (i.e., intake ports) formed in the outer shell  5  through the pair of left and right through holes formed in the impact-on-the-head absorbing liner  11 . 
   (2) Shutter Mechanism for Back Head Side Ventilator Mechanism 
   In the second embodiment, as shown in  FIGS. 13 and 15 , a pair of left and right shutter mechanisms  56  that can close and open a pair of left and right second exhaust paths  73  are provided. Since no shutter mechanism that can close and open a first exhaust path  72  is provided, the first exhaust path  72  (in other words, a pair of left and right ventilation openings  53   a  and  53   b ) is always open. The ventilation openings  53   a  and  53   b  are covered from the outside with a ventilation opening forming member  51  serving also as a stabilizer constituting member. Hence, rain water or the like hardly enters the outer shell  5  from the ventilation openings  53   a  and  53   b.    
   The pair of left and right shutter mechanisms  56  can be axi-symmetric to each other with respect to the center line  75  as an axis of symmetry. Accordingly, in the following description, the right shutter mechanism  56  will be described in detail, and a detailed description on the left shutter mechanism  56  will be omitted. 
   As shown in  FIG. 15 , the right shutter mechanism  56  has a shutter member  101  serving also as an operating member, and an attaching member  102  for attaching the shutter member  101  to the outer surface of the outer shell  5  and/or the inner surface of the ventilation opening forming member  51 . The right shutter mechanism  56 , except for an operating tap  101   a  formed on the shutter member  101 , is covered with the ventilation opening forming member  51 , the inner periphery of which is attached to the outer surface of the outer shell  5  by adhesion with an adhesive or the like. Therefore, the ventilation opening forming member  51  also serves as a cover member for the pair of left and right shutter mechanisms  56 . 
   As shown in  FIGS. 15 and 16 , the attaching member  102  can be a longitudinal plate body extending substantially along the longitudinal direction of a V-shaped projecting ridge  66  of the ventilation opening forming member  51 . A pair of front and rear through holes  103   a  and  103   b  are formed at the front and rear ends, respectively, of the attaching member  102 . The attaching member  102  is fixed to the inner surface of the ventilation opening forming member  51  by screwing with a pair of front and rear attaching screws (not shown) inserted in the through holes  103   a  and  103   b  from their inner sides. In addition to or in place of screwing, the attaching member  102  may be mounted on the outer surface of the outer shell  5  and/or the inner surfaces of the ventilation opening forming member  51  with an adhesive or the like. 
   As shown in  FIG. 16 , a recess  104  is formed in the outer surface of the attaching member  102  for accommodating the shutter member  101 , except for the operating tap  101   a , to be slidable forward and backward substantially in the longitudinal direction. A ventilation opening  105  is formed near the front end of the recess  104 . The ventilation opening  105  corresponds to a ventilation opening  52   b  of the outer shell  5  and a ventilation opening  54   b  of the ventilation opening forming member  51 . 
   As shown in  FIG. 16 , the attaching member  102  has, from its front end toward rear end along the recess  104 , a projection  106  as a stopper in the forward/backward movement, a pair of left and right notches  107   a  and  107   b  for click in the forward movement, a pair of left and right notches  108   a  and  108   b  for click in the backward movement, and a pair of left and right longitudinal protrusions  109   a  and  109   b . The protrusions  109   a  and  109   b  project into the recess  104  from its edges. As shown in  FIG. 18 , a pair of left and right ridge grooves  110   a  and  110   b  are formed in the inner side surface of the attaching member  102  to correspond to the protrusions  109   a  and  109   b , respectively. Hence, the shutter member  101  is accommodated in the recess  104  of the attaching member  102  such that its pair of left and right target guide portions  111   a  and  111   b  can slide forward and backward along the inner side surfaces of the protrusions  109   a  and  109   b  (in other words, the bottom surfaces of the ridge grooves  110   a  and  110   b ), respectively. 
   As shown in  FIG. 17 , the shutter member  101  has a pair of left and right projections  112   a  and  112   b  for clicking, to engage with the pair of left and right notches  107   a  and  107   b  in the forward movement and with the pair of left and right notches  108   a  and  108   b  in the backward movement. The shutter member  101  also has a longitudinal notch  113  extending substantially in the longitudinal direction of the shutter member  101 , in order to regulate the range of the relative movement of the stopper projection  106  of the attaching member  102  relative to the shutter member  101 . Furthermore, in order to impart elasticity to the pair of left and right projections  112   a  and  112   b , the shutter member  101  has one or a plurality of slits  114   a  and  114   b  which extend substantially in the longitudinal direction between the projections  112   a  and  112   b  and can be through holes. 
   Therefore, while the ventilation opening  52   b  of the outer shell  5  and the ventilation opening  54   b  of the ventilation opening forming member  51  are open as shown in  FIG. 15 , when the operating tap  101   a  of the shutter member  101  which is exposed to the outside through an operating tap slit  60  of the ventilation opening forming member  51  is operated in the forward direction, the shutter member  101  moves forward. Thus, a shielding plate portion  115  of the shutter member  101  closes the ventilation opening  52   b  of the outer shell  5  and/or the ventilation opening  54   b  of the ventilation opening forming member  51 . Hence, the ventilation opening  52   b  and/or  54   b  changes from the open state to the closed state. 
   As described above, the ventilation opening  52   b  and/or  54   b  is closed or opened in accordance with the forward or backward movement of the operating tap  101   a . Thus, the pair of left and right second exhaust paths  73  can be selectively or both closed or opened. 
   (3) Ventilation Opening Forming Member Serving Also As Stabilizer Constituting Member 
   The connected portion  70  of the ventilation opening forming member  51  serving also as the stabilizer constituting member is notched to leave its left and right ends, as shown in FIG.  15 . The ventilation openings  55   a  to  55   c  formed in the step surface  64  of the ventilation opening forming member  51  in the first embodiment described above are omitted. A notch  121  which is long in the left-to-right direction is formed along that end of the step surface  64  which is opposite to an air current deflection surface  63 . Hence, as shown in  FIGS. 11  to  13  and  FIG. 15 , a slit  122  serving as an exhaust opening like the ventilation openings  55   a  to  55   c  is formed between that end of the step surface  64  which is opposite to the air current deflection surface  63  and the outer surface of the outer shell  5 . According to the second embodiment, the exhaust opening  122  having a large open area can be formed in the step surface  64  with a comparatively simple manufacturing process, and the strength of the step surface  64  (and accordingly of the ventilation opening forming member  51 ) does not decrease particularly. 
   Different from the first embodiment described above, a two-way forked projecting ridge  66  of each of a pair of left and right air current divider portions  62   a  and  62   b  of the ventilation opening forming member  51  is formed of a comparatively thin V-shaped band-like portion having substantially the same shape as a V-shaped step surface  69 . Hence, a V-shaped peripheral portion  68  of each two-way forked projecting ridge  66  is constituted by the outer peripheral portion of the V-shaped band-like portion, and has substantially the same shape as that of the V-shaped step portion  69  except that the peripheral portion  68  is reversed. 
   Furthermore, bottom surfaces  67  of the air current divider portions  62   a  and  62   b  have bulges  123  which bulge outwardly in the form of an arc immediately behind ventilation openings  54   a  and  54   b  to surround the ventilation openings  54   a  and  54   b , respectively. 
   In item 1(4) (item of “Back Head Side Ventilator Mechanism”) described above, concerning the average angle formed by the air current deflection surface  63  and step surface  64 , other angles, lengths and width of the first embodiment, the numerical values of the embodiment shown in the drawings, preferable numerical value ranges and more preferable numerical value ranges are described. Such angles, lengths and widths in the second embodiment may differ from those of the first embodiment slightly or to a certain degree, but their preferable numerical value ranges and their more preferable numerical value ranges can be substantially the same as those of the first embodiment described above. 
   (4) Exhaust Opening in Occiput Region of Outer Shell 
   As shown in  FIGS. 11  to  13 , a pair of left and right ventilation openings  92   a  and  92   b  are formed in the lower portion of the occiput region of the outer shell  5 . The pair of left and right ventilation openings  92   a  and  92   b  can be slits which are inclined from their upper ends toward their lower ends to the outer left side and outer right side, respectively, and which are formed of through holes. The impact-on-the-head absorbing liner  11  (in other words, the main liner member  22 ) has a pair of left and right ventilation holes (not shown) to respectively correspond to the ventilation openings  92   a  and  92   b . These ventilation holes can be substantially horizontal circular through holes which are inclined from the inner surface toward the outer surface of the main liner member  22  slightly downward and slightly backward, respectively. The outer surface of the main liner member  22  which opposes these ventilation holes can be covered with an air-permiable fabric member (not shown) such as a porous unwoven fabric. 
   Hence, air on the inner side of the impact-on-the-head absorbing liner  11  is discharged to the outside sequentially through the above-mentioned pair of left and right ventilation holes and the pair of left and right ventilation openings  92   a  and  92   b . Thus, the above-mentioned ventilation holes and the ventilation openings  92   a  and  92   b  serve as exhaust holes and exhaust openings, respectively. 
   (5) Ventilation Opening and Ridge Groove of Outer Shell and Impact-On-The-Head Absorbing Liner 
   In the second embodiment, as described in the above item (1) (item of “Front Head Side Ventilator Mechanism”), for the sake of the front head side ventilator mechanism  91 , a pair of left and right ventilation openings are formed in the outer shell  5 , and a pair of left and right through holes communicating with the pair of left and right ventilation openings are formed in the impact-on-the-head absorbing liner  11 . 
   In the second embodiment, for the sake of the forehead ventilator mechanism  9 , a ventilation opening  37  is formed in the outer shell  5 , and a through hole (not shown) communicating with the ventilation opening  37  is formed in the impact-on-the-head absorbing liner  11  (in other words, main liner member  22 ). The ventilation opening  37  and the above-mentioned through hole for the forehead ventilator mechanism  9  correspond to the ventilation openings and the through holes for the front head side ventilator mechanism  91 , and need not communicate with the ventilation holes  28  and  30 , but can be independent of the communication holes  28  and  30 . 
   Furthermore, in the second embodiment, a pair of left and right through holes (not shown) which are not formed in the first embodiment described above are formed in the main liner member  22  so as to communicate with the ventilation holes  28 . More specifically, the pair of left and right through holes are formed in the main liner member  22  so as to be continuous to outer ridge grooves  24   a  and  24   b  at locations slightly in front of a pair of left and right through holes  31   a  and  31   b.    
   In the second embodiment, different from the first embodiment described above, a pair of left and right inner ridge grooves  26   a  and  26   b  of the main liner member  22  extend long continuously forward to portions where they communicate with a pair of left and right through holes for the front head side ventilator mechanism  91 . Different from the first embodiment described above, the pair of left and right outer ridge grooves  24   a  and  24   b  of the main liner member  22  extend continuously to the lower end of the occiput region of the main liner member  22 . A pair of left and right through holes  25   a  and  25   b  of the main liner member  22  are formed at portions slightly in front of the terminal ends of the pair of left and right outer ridge grooves  24   a  and  24   b . The through holes  25   a  and  25   b  do not communicate with the ridge grooves  26   a  and  26   b  on the inner surface of the main liner member  22 , but are independent of the inner ridge grooves  26   a  and  26   b.    
   3. Third Embodiment 
   The third embodiment will be described with reference to FIG.  19 . The third embodiment can be substantially the same as the first embodiment described above except that the practical structure of a shutter mechanism  56  of a back head side ventilator mechanism  8  is different and accordingly the practical shape of a ventilation opening forming member  51  serving also as a stabilizer constituting member is slightly different. Hence, in the following description, only these differences will be described, and a description on portions that are common to the first and third embodiments will be omitted. 
   The shutter mechanism  56  can close or open all of a pair of left and right ventilation openings  52   a  and  52   b  and a pair of left and right ventilation openings  53   a  and  53   b  simultaneously by moving a single operating tap  131   a  of a single operating member  131  forward and backward. The shutter mechanism  56  has the single operating member  131 , an attaching plate or attaching member (i.e., the auxiliary plate described above)  132 , with which the operating member  131  is attached to an outer shell  5 , and a pair of left and right auxiliary shutter members  133   a  and  133   b.    
   The operating member  131  serves also as a main shutter member, and has a pair of left and right shielding plate portions  134   a  and  134   b  projecting forward, and the operating tap  131   a  projecting backward. The operating member  131  has a pair of left and right guide slits  135   a  and  135   b  extending substantially along the left-to-right direction, a guide slit  136  with a position holding function formed between the slits  135   a  and  135   b  and extending substantially along the left-to-right direction, and an auxiliary slit  137  extending between the slit  136  and operating tap  131   a  substantially along the left-to-right direction. An elastic deformable portion  138  curved toward the slit  136  is formed between the guide slit  136  with the position holding function and the auxiliary slit  137 . Hence, the guide slit  136  has a function of holding in position a guide projection  142  (to be described later). 
   The attaching plate  132  is attached to the outer surface of the outer shell  5  by, e.g., adhesion with an adhesive. The attaching plate  132  has a pair of left and right guide projections  151   a  and  151   b  which oppose the pair of left and right guide slits  135   a  and  135   b , respectively, and the guide projection  142  with the position holding function which opposes the slit  136 . The guide projection  142  has a groove  142   a  extending substantially along the direction of forward/backward movement of an operating member  131 . Hence, the guide projection  142  itself has elasticity, and accordingly a position holding function. The guide projections  151   a ,  151   b  and  142  are inserted in the slits  135   a ,  135   b  and  136 , respectively, so as to slidable relative to them. 
   A portion near one end of each of the pair of left and right auxiliary shutter members  133   a  and  133   b  is pivotally axially supported near the corresponding one of the left and right ends of the operating member  131  by a corresponding one of shafts  143   a  and  143   b . The auxiliary shutter members  133   a  and  133   b  can be elongated plate bodies which are substantially curved forward like arcs. 
   A pair of left and right slits  144   a  and  144   b  are formed in the operating member  131  in the vicinities of the shafts  143   a  and  143   b , respectively. The guide slits  144   a  and  144   b  form substantially arcs about the shafts  143   a  and  143   b  as the centers, respectively. Guide projections  145   a  and  145   b  formed on the pair of left and right auxiliary shutter members  133   a  and  133   b  are inserted in the arcuate slits  144   a  and  144   b , respectively, such that they can slide relative to them. 
   The outer shell  5  has left and right pairs of support rods  146   a  and  147   a , and  146   b  and  147   b  for supporting the pair of left and right auxiliary shutter members  133   a  and  133   b , such that they oppose the intermediate portions of the auxiliary shutter members  133   a  and  133   b , respectively. The support rods  146   a  and  147   a , and  146   b  and  147   b  oppose each other at distances substantially corresponding to the widths of the intermediate portions of the auxiliary shutter members  133   a  and  133   b , respectively. The opposing surfaces of the support rods  146   a  and  147   a , and  146   b  and  147   b  form substantially semicircular cylindrical convex surfaces. 
   Shielding plate portions  148   a  and  148   b  are formed at the free ends of the auxiliary shutter members  133   a  and  133   b  to correspond to the ventilation openings  52   a  and  52   b , respectively, of the outer shell  5 . A ventilation opening  149  is formed in the auxiliary shutter member  133   b  to be adjacent to the shielding plate portion  148   b . When the auxiliary shutter member  133   b  moves backward to the open state position, the ventilation opening  149  overlaps the ventilation opening  52   b  of the outer shell  5  to open it, as shown in FIG.  19 . 
   The distance between the inner surface of the ventilation opening forming member  51  (but near the outer periphery of the ventilation opening  52   b ) and the outer surface of the outer shell  5  can be set to substantially coincide with the thickness of that portion of the auxiliary shutter member  133   b  which is near the outer periphery of the ventilation opening  149 . In this case, the second exhaust path  73  on the right side described in the above item 1(4) (item of “Back Head Side Ventilator Mechanism”) is comprised of only the right ventilation opening  52   b , ventilation opening  149 , and right ventilation opening  54   b . Thus, air flowing in this second exhaust path  73  will not undesirably diffuse in a ventilation space  71 . Note that a second exhaust path  73  on the left side can have the same arrangement as this. In this case, the free end of the left auxiliary shutter member  133   a  may be extended from the shielding plate portion  148   a  to form an extension  150 , as indicated by a chain line in  FIG. 19 , and a ventilation opening  151  may be formed in the extension  150  to correspond to the ventilation opening  149 . 
   The ventilation opening forming member  51  in the third embodiment can be substantially the same as the ventilation opening forming member  51  of the first embodiment described above, except that a slit  139  for the operating tap  131   a  is formed, in place of a pair of left and right operating tap slits  60 , in a step surface  64  between ventilation openings  55   a ,  55   b  and  55   c , and a connecting portion  70 . 
   Therefore, while the ventilation openings  52   a ,  52   b ,  53   a  and  53   b  of the outer shell  5  are open as shown in  FIG. 19 , when the operating tap  131   a  of the operating member  131  which is exposed to the outside through the operating tap slit  139  of the ventilation opening forming member  51  is moved forward to the left (right in FIG.  19 ), the main shutter member  131  serving also as the operating member moves forward to the left because of the guide function of the linear forward/backward movement of the guide slits  135   a ,  135   b  and  136  and the guide projections  151   a ,  151   b  and  142 . Hence, the shielding plate portions  134   a  and  134   b  of the main shutter member  131  close the ventilation openings  53   a  and  53   b  of the outer shell  5  from the outer surface. Accordingly, the ventilation openings  53   a  and  53   b  change from the open state to the closed state. When the main shutter member  131  moves forward, the auxiliary shutter members  133   a  and  133   b  pivot slightly clockwise and counterclockwise, respectively, in  FIG. 19  about the shafts  143   a  and  143   b  as the fulcrums while they are being supported at their intermediate portions by the support rods  146   a  and  147   a  and  146   b  and  147   b  and being guided by the guide slits  144   a  and  144   b  and guide projections  145   a  and  145   b . Accordingly, the shielding plate portions  148   a  and  148   b  of the auxiliary shutter members  133   a  and  133   b  close the ventilation openings  52   a  and  52   b , respectively, of the outer shell  5  from their outer surfaces. As a result, the ventilation openings  52   a  and  52   b  change from the open state to the closed state. 
   As described above, the ventilation openings  52   a ,  52   b ,  53   a  and  53   b  are closed or opened simultaneously in accordance with the forward/backward operation of the single operating tap  131   a . Therefore, the first exhaust path  72  and the pair of left and right second exhaust paths  73  can all be closed or opened simultaneously. 
   The third embodiment described above is substantially the same as the first embodiment described above, except that the shutter mechanism  56  of the back head side ventilator mechanism  8  has a different practical structure and accordingly the ventilation opening forming member  51  serving also as the stabilizer constituting member has a slightly different practical shape. However, the third embodiment described above can be substantially the same as the second embodiment described above, except that the shutter mechanism  56  of the back head side ventilator mechanism  8  has a different practical structure and accordingly the ventilation opening forming member  51  serving also as the stabilizer constituting member has a slightly different practical shape. 
   So far the first, second and third embodiments of the present invention have been described in detail. The present invention is not limited to these embodiments, and various types of changes and modifications can be made on the basis of the spirit of the invention described in claims. 
   For example, in the above embodiments, the single stabilizer portion  61  serving also as the ventilation opening forming portion is formed at the central portion in the left-to-right direction of the ventilation opening forming member  51  serving also as the stabilizer constituting member, and the pair of left and right air current divider portions  62   a  and  62   b  are formed on the two sides in the left-to-right direction of the ventilation opening forming member  51 . Conversely, a single air current divider portion may be formed at the central portion in the left-to-right direction of the ventilation opening forming member  51  serving also as the stabilizer constituting member, and a pair of left and right stabilizer portions serving also as ventilation opening forming members may be formed on the two sides in the left-to-right direction of the ventilation opening forming member  51 . 
   In the above embodiments, the pair of left and right ventilation holes  30  formed between the outer surface  23   b  of the impact-on-the-head absorbing liner  11  and the inner surface of the outer shell  5  communicate with the first exhaust path  72 , and the pair of left and right ventilation holes  28  formed between the main liner member  22  and outer auxiliary liner member  23 , and the left and right pairs of through holes  31   a  and  31   b , and  32   a  and  32   b  of the impact-on-the-head absorbing liner  11  communicate with the pair of left and right second exhaust paths  73 . Conversely, the pair of left and right ventilation holes  30  may communicate with the pair of left and right second exhaust paths  73 , and the pair of left and right ventilation holes  28  and the left and right pairs of through holes  31   a  and  31   b , and  32   a  and  32   b  may respectively communicate with the first exhaust path  72 . 
   In the above embodiments, the step surface  64  of the stabilizer  61  serving also as the ventilation opening forming member extends from the rear end of the air current deflection surface  63  substantially toward the outer surface of the outer shell  5 . However, it suffices if the step surface  64  extends from the vicinity of the rear end of the air current deflection surface  63  substantially toward the outer surface of the outer shell  5 . For example, in the state shown in  FIG. 5 , the air current deflection surface  63  may project like eaves over the step surface  64 . 
   In the above embodiments, the substantially V-shaped projecting ridge  66  is formed on each of the pair of left and right air current divider portions  62   a  and  62   b . The projecting ridge  66  need not have a substantially V shape, but may have another substantially two-way forked shape such as a substantially U shape. The preferable numerical value ranges and more preferable numerical value ranges already described concerning the substantially V-shaped projecting ridge  66  substantially apply to a case wherein the projecting ridge  66  has another such substantially two-way forked shape. 
   In the above embodiments, the ventilation openings  52   a  and  52   b , and  53   a  and  53   b  formed in the outer shell  5  are closed by the shutter mechanism or mechanisms  56 , so that the first exhaust path  72  and the pair of left and right second exhaust paths  73  are closed by the shutter mechanism or mechanisms  56 . However, this arrangement is not always necessary. For example, the ventilation openings  54   a  and  54   b , and  55   a  to  55   c  formed in the ventilation opening forming member  51  may be closed by the shutter mechanism or mechanisms  56 . 
   In the above embodiments, the present invention is applied to the full-face-type helmet  1 . The present invention can also be applied to other types of helmets such as a jet-type helmet, a semi-jet-type helmet or a full-face-type helmet serving also as a jet-type helmet, the chin portion of which can be raised.