Abstract:
A helmet with an air supply/exhaust hole serving as a hole to be shared by an air supply hole portion for an air supply path for introducing air outside an outer shell into a head protecting body, and an exhaust hole portion for an exhaust path for exhausting air in the head protecting body to an outside of the outer shell. According to this helmet, a predetermined region in the head protecting body can be ventilated well. The air supply hole portion for the air supply path and the exhaust hole portion for the exhaust path can be formed in the outer shell easily. An outer shell with a high strength can be obtained easily. Design limitations on the outer shell can be reduced.

Description:
TECHNICAL FIELD 
     The present invention relates to a helmet having a head protecting body with an outer shell, in which an air supply path for introducing air outside the outer shell into the head protecting body is formed in the head protecting body, and an exhaust path for exhausting air in the head protecting body outside the outer shell is formed in the head protecting body apart from the air supply path. 
     BACKGROUND OF THE INVENTION 
     Conventionally, as a helmet to be worn by the head of a helmet wearer (to be referred to as a “wearer” hereinafter) such as the rider of a motor cycle, a full-face-type helmet is known. Usually, the cap-shaped head protecting body of such a full-face-type helmet has a chin ventilator mechanism under a window opening formed to oppose the face of the wearer. The chin ventilator mechanism has a chin air supply path extending from an air supply port or air supply notch formed in the chin region (i.e., a region opposing the chin of the wearer) of the outer shell. In addition to the chin air supply path, a breath guard is attached to the head protecting body between the mouth of the wearer and a shield plate in order to prevent the shield plate from being fogged by the breath exhaled by the wearer. 
     In such a conventional helmet, outer air is introduced, near the lower end of the inner surface of the shield plate, into the head protecting body through the chin air supply path. The introduced outer air is let to flow upward along the inner surface of the shield plate, and the breath guard prevents the breath exhaled by the wearer from being directly directed toward the shield plate, thereby preventing fogging of the shield plate. 
     In this conventional helmet, when the humidity is very high due to a rainfall, the shield plate is inevitably fogged due to the breath exhaled by the wearer, and anti-fogging of the shield plate cannot be performed well. Therefore, as a countermeasure, in the conventional helmet, a pair of right and left exhaust holes may be formed in the chin region of an impact absorbing liner. A pair of right and left exhaust holes may be formed in a corresponding chin region of an outer liner, and a pair of right and left chin exhaust paths may be formed to extend from the liner-side exhaust holes to the outer-shell-side exhaust holes. 
     In the conventional helmet with the above arrangement, the air supply hole for the chin air supply path must be formed at substantially the central portion of the chin region of the outer shell, and the pair of right and left air supply holes for the pair of right and left chin air supply paths must be formed on the right and left sides of the chin region of the outer shell. This requires a complicated process of forming the air supply hole and exhaust holes in the outer shell, and it is cumbersome and time-consuming to obtain an outer shell with a high strength. Also, the outer shell has a large design limitation. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to correcting the drawbacks described above of the conventional helmet effectively with a comparatively simple arrangement. 
     It is, therefore, the main object of the present invention to provide a helmet in which an air supply path for introducing air outside an outer shell into a head protecting body and an exhaust path for exhausting air in the head protecting body outside the outer shell are formed in the head protecting body apart from and adjacent to each other, so that air is supplied to and exhausted from a predetermined region in the head protecting body simultaneously, thereby ventilating the predetermined area well. 
     It is another object of the present invention to provide a helmet in which since an air supply hole for an air supply path and an exhaust hole for an exhaust path need not be separately formed in an outer shell independently of each other, the process of forming both an air supply hole portion for an air supply path and an exhaust hole portion for an exhaust path in the outer shell can be comparatively simple, an outer shell with a high strength can be obtained comparatively easily, and design limitation on the outer shell can be made comparatively small. 
     It is still another object of the present invention to provide a helmet in which an air supply path can have a comparatively simple structure and outer air can flow in the air supply path in a good state. 
     It is still another object of the present invention to provide a helmet in which an air exhaust path can have a comparatively simple structure. 
     It is still another object of the present invention to provide a helmet in which since air is supplied to and exhausted from the chin region in the head protecting body simultaneously, the chin region can be ventilated well, so that even when the humidity is very high due to a rainfall, the shield plate can be effectively prevented from being fogged by the breath exhaled by the wearer. 
     It is still another object of the present invention to provide a helmet in which air in the head protecting body can be let to flow out effectively from the air outlet port of a head air path, so that the interior of the head protecting body can be ventilated better. 
     The present invention relates to a helmet comprising a head protecting body with an outer shell, wherein an air supply path for introducing air outside the outer shell into the head protecting body is formed in the head protecting body, an exhaust path for exhausting air in the head protecting body outside the outer shell is formed in the head protecting body apart from the air supply path, and an air supply/exhaust hole serving as a hole to be shared by an air supply hole portion for the air supply path and an exhaust hole portion for the exhaust path is formed in the outer shell. 
     According to the first aspect of the present invention, one half of the air supply/exhaust hole, which is on a central side of the helmet in a horizontal direction, forms the air supply hole portion for the air supply path, and the other half of the air supply/exhaust hole, which is opposite to the central side of the helmet in the horizontal direction, forms the exhaust hole portion for the exhaust path. 
     The present invention and the first aspect described have, according to the second aspect, an air supply path main body which forms the air supply path together with the air supply hole portion of the air supply/exhaust hole, and an air supply path forming member used for forming the air supply path main body is disposed on an inner surface of a chin region of the outer shell. 
     In the second aspect of the present invention, according to the third aspect, the air supply path forming member has at least three (more preferably at least four) straightening air supply paths. 
     In the second and third aspects of the present invention, according to the fourth aspect, an air supply port forming member with an inner air supply port forming portion is arranged between the outer shell and the air supply path forming member. 
     In the fourth aspect of the present invention, according to the fifth aspect, a shutter member for opening/closing a ventilation port of the inner air supply port forming portion is provided to the air supply port forming member. 
     The second to fifth aspects have, according to the sixth aspect, an exhaust path main body for constituting the exhaust path together with the exhaust hole portion of the air supply/exhaust hole, and an impact absorbing liner arranged inside the outer shell, and the exhaust path main body comprises a recess formed in an outer surface of the impact absorbing liner, an aperture formed in the impact absorbing liner to be continuous to the recess, and a partitioning plate of the air supply path forming member. 
     In the sixth aspect, according to the seventh aspect, a bottom surface of the recess forms a slant surface slanting backward toward that side of the helmet which is opposite to a central longitudinal section line side, and the slant surface has a slant angle within a range of 0.5° to 5° (more preferably 1° to 3°). 
     In the sixth and seventh aspects of the present invention, according to the eighth aspect, at least part of that portion of an outer surface of the partitioning plate, which forms the exhaust path main body, forms a slant surface slanting forward toward that side of the helmet which is opposite to the central longitudinal section line side, and the slant surface has a slant angle within a range of 0.5° to 5° (more preferably 1° to 3°). 
     In the first to eighth aspects of the present invention, according to the ninth aspect, the air supply/exhaust hole comprises a pair of left and right air supply/exhaust holes in the chin region of the outer shell, the air supply path is formed at a substantially central portion in a horizontal direction of said chin region of said head protecting body, the exhaust path comprises a pair of left and right exhaust paths on left and right portions of the chin region of the head protecting body, those halves of the pair of left and right air supply/exhaust holes, which are on the central side in the horizontal direction, form air supply hole portions for the air supply path, and those halves of the pair of left and right air supply/exhaust hole, which are opposite to the central side in the horizontal direction, form exhaust hole portions for the pair of left and right exhaust paths. 
     In the ninth aspect of the present invention, according to the 10th aspect, the air supply path branches into two branches from an end point to a start point thereof. 
     In the sixth to 10th aspects of the present invention, according to the 11th aspect, a fitting opening is formed at a center of a lower portion of the air supply path forming member by notching upward from a lower end of the air supply path forming member, and a fitting projection is formed on the impact absorbing liner, the fitting projection being fitted in the fitting opening. 
     In the ninth to 11th aspects of the present invention, according the 12th aspect, an air outlet port which forms an end point of a head air path is formed in a lower end face of a rear portion of the head protecting body, and a narrow or constricted portion is formed in a rear portion of the outer shell. 
     In the 12th aspect of the present invention, according to the 13th aspect, a slant angle of the narrow or constricted portion near a lower end of the rear portion of the outer shell is in a range of 20° to 40° (more preferably 25° to 35°) on a center line in a right-to-left direction of the outer shell. 
    
    
     The above and other objects, features and advantages of this invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall perspective view of a helmet in an embodiment in which the present invention is applied to a full-face-type helmet; 
     FIG. 2 is a longitudinal sectional view of the helmet shown in FIG. 1; 
     FIG. 3 is a perspective view of the chin ventilator mechanism of the helmet shown in FIG. 1; 
     FIG. 4 is an exploded perspective view of the ventilator constituent members of the chin ventilator mechanism shown in FIG. 3; 
     FIG. 5A is a front view of the left half of the impact-on-the-chin-and-cheek absorbing liner shown in FIG. 3 which is longitudinally taken at the center; 
     FIG. 5B is a cross-sectional view of the left half shown in FIG. 5A; and 
     FIG. 6 is an enlarged longitudinal sectional view of the nape ventilator portion of the head ventilator mechanism shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment in which the present invention is applied to a full-face-type helmet will be described with reference to the accompanying drawings. 
     (1) Description on Entire Helmet 
     As shown in FIGS. 1 and 2, a full-face-type helmet  1  is made up of a full-face-type head protecting cap body  2  to be worn on the head of a wearer, a shield plate  4  capable of opening/closing a window opening  3  formed in the front surface of the head protecting body  2  to oppose the portion (i.e., the face) between the forehead and chin of the wearer, and a pair of right and left chin straps  5  attached to the inside of the head protecting body  2 . As has been known, the shield plate  4  is made of a transparent or translucent hard material such as polycarbonate or another hard synthetic resin. The shield plate  4  is pivotally attached to the head protecting body  2  with a pair of right and left attaching screws  6 . The shield plate  4  closes the window opening  3  at the backward pivoting position shown in FIGS. 1 and 2, and opens the window opening  3  at the forward pivoting position at which 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 . In FIG. 1, a tap  7  is formed on the shield plate  4  and is held by the wearer with his fingers when the wearer is to pivot upward and downward the shield plate  4 . An operating lever  8  is formed on the head protecting body  2  and is operated by the wearer when the wearer is to slightly pivot upward the shield plate  4  located at the backward pivoting position. 
     As shown in FIGS. 1 and 2, the head protecting body  2  is made up of a full-face-type outer shell  11  which forms the circumferential wall of the head protecting body  2 , a lower rim member  12  having a substantially U-shaped cross-section and fixed to the outer shell  11  throughout the lower end of the outer shell  11  with an adhesive or the like, a rim member  14  for a window opening, which has a substantially E-shaped cross-section and is fixed, with an adhesive or the like, to the outer shell  11  throughout the periphery of an window opening  13  formed in the outer shell  11  to form the window opening  3  of the head protecting body  2 , a backing member  15  for the head, which is fixed to the outer shell  11  with an adhesive or the like in contact with the inner surface of the outer shell  11  in a front head region, a top head region, right and left side head regions and a back head region respectively corresponding to the front part, top part, right and left parts and back part of the head of the wearer, and a backing member  16  for the chin and cheek, which is fixed to the outer shell  11  with an adhesive or the like in contact with the inner surface of the outer shell  11  in chin and cheek regions respectively corresponding to the chin and cheeks of the wearer. 
     As is conventionally known, the outer shell  11  can be made of a composite material formed by lining the inner surface of a strong shell body made of a hard synthetic resin, e.g., FRP, with a flexible sheet such as an nonwoven fabric. As is conventionally known, the lower rim member  12  can be made of a soft synthetic resin such as foamed vinyl chloride or synthetic rubber. As is conventionally known, the rim member  14  can be made of an elastic material with high flexibility such as synthetic rubber. 
     As is shown in FIGS. 2 and 6, the backing member  15  is constituted by an impact-on-the-head absorbing liner  21  and a breathing backing cover  22  for the head attached to the impact-on-the-head absorbing liner  21  so as to cover almost its entire inner surface. The backing member  16  is constituted by an impact-on-the-chin-and-cheek absorbing liner  23  and a pair of left and right blockish inside pads  24   a  and  24   b  for the cheeks which are attached to the impact-on-the-chin-and-cheek absorbing liner  23  in contact with the inner surface of the impact-on-the-chin-and-cheek absorbing liner  23  in left and right cheek regions corresponding to the left and right cheeks of the wearer. 
     As is conventionally known, the body portion of each of the impact-on-the-head absorbing liner  21  and impact-on-the-chin-and-cheek absorbing liner  23  can be made of a material with appropriate rigidity and appropriate plasticity such as polystyrene foam or another synthetic resin. As is conventionally known, the body portion of the backing cover  22  can be made of a combination of woven fabric and porous nonwoven fabric formed by laminating layers, each made of an elastic material with high flexibility such as urethane foam or another synthetic resin, on the surface (i.e., the outer surface) opposing the impact-on-the-head absorbing liner  21 , or two side surfaces. 
     As shown in FIGS. 2 and 6, a front-side engaged member  25  and rear-side engaged member  26  are respectively attached to the front and rear end portions of the body portion of the backing cover  22  with a sewing thread, a tape, an adhesive or the like. A front-side engaging member  27  and rear-side engaging member  28  are respectively attached to the front and rear end portions of the body portion of the impact-on-the-head absorbing liner  21  by fixing with rivets and washers or the like, or with an adhesive, a tape or the like to substantially oppose the front- and rear-side engaged members  25  and  26 . A pair of left and right engaged studs (not shown) respectively formed on the front- and rear-side engaged members  25  and  26  on the backing cover  22  side are press-fitted in a pair of left and right engaging apertures (not shown) respectively formed in the front- and rear-side engaging members  27  and  28  on the impact-on-the-head absorbing liner  21  through projection-recess engagement, thereby detachably attaching the backing cover  22  to the impact-on-the-head absorbing liner  21 . 
     As is conventionally known, the front- and rear-side engaged members  25  and  26  of the backing cover  22  and the front- and rear-side engaging members  27  and  28  on the impact-on-the-head absorbing liner  21  can be made of a flexible synthetic resin such as polyethylene. In FIGS. 2 and 6, appropriate numbers of ventilation openings  31  and  32 , and  33  and  34  are formed in the front-side engaged and engaging members  25  and  27  and the rear-side engaged and engaging members  26  and  28 , respectively. 
     The pair of left and right blockish inside pads  24   a  and  24   b  for the cheeks are symmetrical. Thus, the blockish inside pad  24   b  for the right cheek will be described in detail with reference to FIG. 2, and a detailed description on the blockish inside pad  24   a  for the left cheek will be omitted. 
     As shown in FIG. 2, the blockish inside pad  24   b  for the right cheek has a notch  35  to exclude an ear region corresponding to the right ear part of the wearer. Hence, the blockish inside pad  24   b  has a shape corresponding to the right cheek part and its vicinity (excluding the right ear part) of the wearer. The left chin strap  5  is inserted in the notch  35 . As is conventionally known, the blockish inside pad  24   b  may be made up of a thick platelike cushion member (not shown) formed of one or a plurality of flexible, elastic members of material such as urethane foam or another synthetic resin, and a bag-like member  29  covering the cushion member substantially entirely like a bag. 
     FIG. 5A is a front view of the left half of the impact-on-the-chin-and-cheek absorbing liner  23  with a symmetric shape (i.e., an axi-symmetrical shape), which is longitudinally taken at a central longitudinal section line  40  of the full-face-type helmet  1 , and FIG. 5B is a cross-sectional view of the same. As shown in FIG. 5B, a pair of right and left support members  41  are attached to the inner surface of the main body portion of the impact-on-the-chin-and-cheek absorbing liner  23  with an adhesive or the like. An appropriate number of female portions (i.e., female hooks)  42  of round hooks which form engaging holes are attached to the support members  41 . An appropriate number of male portions (i.e., male hooks) of round hooks which form engaging projections are attached to the outer surface of the blockish inside pad  24   b . The male hooks (not shown) are press-fitted in the female hooks  42  by recess-projection engagement, thereby detachably attaching the blockish inside pad  24   b  for the cheek to the impact-on-the-chin-and-cheek absorbing liner  23 . 
     Referring to FIG. 5B, openings  43  and  44  are formed in the body portion of the impact absorbing liner  23  and the support members  41  so the chin straps  5  are inserted through them. In FIGS. 5A and 5B, a central or front recess  45  is formed in almost the central portion of the front surface of the body portion of the impact-on-the-chin-and-cheek absorbing liner  23 , and an exhaust hole  46  is formed on the liner  23  side to be continuous to the front recess  45 . The front recess  45  and the exhaust holes  46  on the liner  23  side will be described later in detail. 
     The head protecting body  2  has a chin ventilator mechanism  51  corresponding to the chin region of the backing member  16  for the chin and cheek, and a head ventilator mechanism  52  corresponding to the backing member  15  for the head. The chin ventilator mechanism  51  and head ventilator mechanism  52  will be described hereinafter separately. 
     (2) Description on Chin Ventilator Mechanism  51   
     The chin ventilator mechanism  51  has three types of chin ventilator constituent members consisting of an air supply path forming member  53 , a shutter member  54  and an air supply port forming member  55 , as shown in FIGS. 3 and 4. Each of the three types of ventilator constituent members  51  to  53  can be made of a material with appropriate elasticity and appropriate rigidity such as polycarbonate, polyacetal, ABS, nylon, or any other synthetic resin. 
     As shown in FIGS. 1,  2 ,  3  and  4 , the air supply path forming member  53  has a member main body  56  extending to be curved (a curve protruding outward) substantially arcuately in the horizontal direction substantially along the window opening  13  of the outer shell  11 . A substantially square opening  57  is formed at the substantial center of the lower portion of the member main body  56  by notching upward from the lower end. A pair of left and right attaching bosses  58   a  and  58   b  are formed on the front surfaces of the right and left upper portions of the member main body  56 . A bend  59  which is bent substantially forward is formed on the upper end of the member main body  56 , and an inverted U-shaped bend  60  which is bent substantially forward is formed on the periphery of the opening  57 . The left and right sides of the member main body  56  are slightly flexed obliquely forward to form a pair of left and right bends  61   a  and  61   b . The pair of left and right attaching bosses  58   a  and  58   b  are formed on the upper front surfaces of the pair of left and right bends  61   a  and  61   b , respectively. 
     As shown in FIGS. 3 and 4, a plurality of guide plates project from each of the left and right sides of the front surface of the member main body  56  of the air supply path forming member  53 . In the embodiment shown in FIGS. 3 and 4, two sets of three different-length guide plates  62   a ,  63   a  and  64   a , and  62   b ,  63   b  and  64   b  are formed on the left and right sides of the front surface of the member main body  56  such that their lengths gradually decrease from the central side to the left or right side. Left and right side portions  60   a  and  60   b  of the inverted U-shaped bend  60  also serve as guide plates. Hence, three (in other words, a plurality of) left straightening air supply paths  65   a ,  66   a  and  67   a  are formed 
     1) between the left portion  60   a  of the inverted U-shaped bend  60  and the guide plate  62   a,    
     2) between the guide plates  62   a  and  63   a , and 
     3) between the guide plates  63   a  and  64   a  on the left side of the front surface of the air supply path forming member  53 . Similarly, three (in other words, a plurality of) right straightening air supply paths  65   b ,  66   b  and  67   c  are formed on the right side of the front surface of the air supply path forming member  53 . The total number of the straightening air supply paths formed on the air supply path forming member  53  is preferably at least three, and is more preferably at least four. 
     Of the member main body  56  of the air supply path forming member  53 , portions  56   a  and  56   b  located on the left and right sides of the opening  57  (i.e., the lower left and right portions of the member main body  56 ) are slightly curved to protrude arcuately backward from the upper end to the lower end. A pair of left and right engaged projections  68   a  and  68   b  are formed, near the bend  59 , on the member main body  56  of the air supply path forming member  53 . Also, engaged plates  69   a  and  69   b  projecting substantially upward are formed near the left and right sides of an upper projecting ridge  60   c  of the inverted U-shaped bend  60 . 
     As shown in FIG. 4, the pair of left and right guide plates  62   a  and  62   b , which are the longest of the guide plates  62   a  to  64   a  and  62   b  to  64   b , respectively have steps  70  formed by notching near their upper ends. The steps  70  position and hold the lower end of a member main body  71  of the air supply port forming member  55  (to be described later). As the pair of left and right guide plates  64   a  and  64   b , which are the shortest, do not extend to the bends  61   a  and  61   b  of the left and right lower portions  56   a  and  56   b  of the member main body  56 , the bends  61   a  and  61   b  serve not only as partitioning plates for defining a chin air supply path  121  and chin exhaust paths  122   a  and  122   b , as will be described later, but also as deflecting plates  95   a  and  95   b  for deflecting the air flow from the central side to the left and right outward. 
     As shown in FIGS. 1,  2 ,  3  and  4 , the air supply port forming member  55  has the member main body  71  with screw insertion holes  72   a  and  72   b  near its left and right ends and extending to be curved (a curve protruding outward) substantially arcuately in the horizontal direction substantially along the member main body  56  of the air supply path forming member  53 . The central portion of the front surface of the member main body  71  projects outward (i.e., toward the front surface), thus forming a projecting surface  73 . The inner surface (i.e., the rear surface) of the projecting surface  73  forms a recess. The upper half of the front surface of the member main body  71  is thinner than the lower half thereof and thus forms a thin-walled portion  71   a . The screw insertion holes  72   a  and  72   b  are formed near the left and right ends of the lower half of the front surface of the member main body  71 . 
     As shown in FIGS. 3 and 4, an inner air supply port forming portion  74  is formed at the upper end of the thin-walled portions  71   a  of the member main body  71  of the air supply port forming member  55  to extend substantially horizontally along the upper end of the thin-walled portions  71   a , such that it protrudes almost backward to be flexed slightly obliquely upward in the backward direction. The inner air supply port forming portion  74  extends forward to form a projecting ridge  74   a . As the inner air supply port forming portion  74  has a comb-like shape with a large number of notches  75  formed in its rear end side, a large number of projections  76  are formed between the notches  75 . The notches  75  form a plurality of (e.g., three) inner air supply ports on each of the right and left sides. Of the large number of projections  76 , a pair of left and right left projections  76   b  and  76   c  which are most adjacent to a central projection  76   a  has engaging holes (not shown), formed in their rear surfaces, to fit on the pair of left and right engaged studs  68   a  and  68   b , respectively, of the air supply path forming member  53 . 
     As shown in FIG. 4, a substantially U-shaped hanging portion  77  is integrally formed at the central portion of the member main body  71  of the air supply port forming member  55 , and accordingly an opening  78  is formed between the member main body  71  and hanging portion  77 . Also, a waved spring  79  is integrally formed on the rear surface of the hanging portion  77  across the opening  78  substantially horizontally, and accordingly the opening  78  is halved into an upper and lower openings  78   a  and  78   b . An inverted U-shaped projecting ridge  80  is formed on the periphery of the upper opening  78   a  along its upper side and left and right sides. A projecting ridge  81  with a groove (not shown) substantially at its center is integrally formed along the lower end of the hanging portion  77  such that it protrudes backward. The spring  79  has a substantially L-shaped longitudinal section and forms a step  79   a  on its outer surface (i.e., front surface). 
     As shown in FIGS. 3 and 4, the shutter member  54  has a member main body  82  extending to be curved (a curve protruding outward) substantially arcuately in the horizontal direction substantially along the member main body  71  of the air supply port forming member  55 . An opening/closing shutter portion  83  is provided to the upper end of member main body  82  of the shutter member  54  to extend substantially horizontally along the upper end of the member main body  82 , such that it protrudes almost backward to be flexed slightly obliquely upward in the backward direction. As the opening/closing shutter portion  83  has a comb-like shape and a large number of notches  84  are formed near its rear end to correspond to the notches  75  of the air supply port forming member  55 , a large number of projections  85  are formed between the notches  84 . The notches  84  form a plurality of (e.g., five) air supply ports, and the projections  85  form a plurality of (e.g., six) blocking portions. 
     As shown in FIG. 4, a substantially square hanging portion  86 , which extends downward, is integrally formed at the substantially central portion of the lower end of the member main body  82  of the shutter member  54 . An engaged stud  87  is integrally formed at the substantially central portion of the lower end of the hanging portion  86 . A connecting portion  88  with a substantially L-shaped longitudinal section is integrally formed on the hanging portion  86  near the lower end of its front surface. The connecting portion  88  extends substantially horizontally from the hanging portion  86  such that it protrudes almost forward to be flexed slightly obliquely downward in the forward direction, and then substantially vertically such that it protrudes almost downward to be flexed slightly obliquely forward in the downward direction. 
     A tap  89  is integrally formed on the lower end of the connecting portion  88  of the shutter member  54 , as shown in FIG. 4, to extend obliquely forward and downward from this lower end. The tap  89  has a notch  90  at its distal end so the wearer can hold the tap  89  with his fingers easily. A stud  91  is integrally formed on the lower surface of the tap  89 , when necessary, so the tap  89  of the shutter member  54  can be slid easily along the outer surface of the outer shell  11 . 
     The three types of chin ventilator constituent members  53  to  55  with the above arrangements are built into the head protecting body  2  on the front surface of the impact-on-the-chin-and-cheek absorbing liner  23 , as shown in FIG.  3 . For this purpose, as shown in FIGS. 3,  5 A and  5 B, the front surface of the impact absorbing liner  23  has the inverted U-shaped front recess  45  substantially corresponding to the shape of the air supply path forming member  53 . That region of the impact absorbing liner  23  which is surrounded by the front recess  45  forms a fitting projection  92  with the original thickness of the impact absorbing liner  23 . 
     As shown in FIGS. 3,  5 A and  5 B, the impact-on-the-chin-and-cheek absorbing liner  23  has a comparatively shallow (i.e., shallower than the front recess  45 ) recess  94  extending substantially horizontally under the front recess  45  and projection  92 . The recess  94  is symmetrical (i.e., axi-symmetrical) about the central longitudinal section line  40  shown in FIGS. 5A and 5B as the axis of symmetry, has a substantial T-shape, and reaches the lower end of the impact absorbing liner  23 . The left and right portions of the upper end of the recess  94  are continuous to the front recess  45 . Hence, rainwater or the like which is to stay in the front recess  45  or at its vicinity is discharged from the lower end of the impact absorbing liner  23  to the outside through the T-shaped recess  94 . 
     As shown in FIGS. 3,  5 A and  5 B, the impact-on-the-chin-and-cheek absorbing liner  23  has a pair of left and right side recesses or exhaust path recesses  93   a  and  93   b  respectively adjacent to lower left and right portions  45   a  and  45   b  of the front recess  45 . The exhaust path recesses  93   a  and  93   b  are continuous to the front recess  45  on the left and right sides of the front recess  45  which are opposite to the central longitudinal section line  40  side (i.e., the lower left and right portions  45   a  and  45   b  of the front recess  45 ). 
     The pair of left and right exhaust path recesses  93   a  and  93   b  are symmetrical (i.e., axi-symmetrical) about the central longitudinal section line  40  of FIGS. 5A and 5B as the axis of symmetry. Thus, the left exhaust path recess  93   a  formed in the left half of the impact-on-the-chin-and-cheek absorbing liner  23  will be described in detail with reference to FIGS. 3,  5 A and  5 B, and a detailed description of the right exhaust path recess  93   b  will be omitted. 
     The exhaust path recess  93   a  has the exhaust hole  46  serving as its start point (i.e., an air inlet port to the exhaust path recess  93   a ), as shown in FIGS. 5A and 5B. The exhaust path recess  93   a  extends from the exhaust hole  46  to the left (i.e., opposite to the central longitudinal section line  40  side, in other words, horizontally outward or outward to the left and right). An upper surface  101 , lower surface  102  and rear surface  103  of the exhaust path recess  93   a  are used to form the chin exhaust path  122   a  (to be described later). The front-side surface (i.e., the front surface) which opposes the rear surface  103  of the exhaust path recess  93   a  is formed by the rear surface of the deflecting/partitioning plate  95   a  of the air supply path forming member  53 , as will be described later. Accordingly, the exhaust path recess  93   a  and partitioning plate  95   a  form the chin exhaust path main body that occupies most of the chin exhaust path  122   a  (to be described later). The chin exhaust path  122   a  is comprised of the chin exhaust path main body and that half of the left air supply/exhaust hole  111   a  of the outer shell  11  which is opposite to the central longitudinal section line  40  side (i.e., horizontally outer side). 
     As shown in FIGS. 5A and 5B, the rear surface (i.e., the bottom surface)  103  of the exhaust path recess  93   a  forms a slant surface slightly slanting backward from the exhaust port  46  to the left (i.e., to the side opposite to the central longitudinal section line  40  side). A slant angle θ 1  of this slant is about 2° in the embodiment shown in FIG. 5B but is generally preferably in the range of 0.5° to 5° from the viewpoint of practicality and is more preferably in the range of 1° to 3°. The front surface (i.e., the outer surface) of the partitioning plate  95   a  which forms a front surface opposing the rear surface  103  of the exhaust path recess  93   a  forms a slant surface, at least near its left end, slanting slightly forward from the exhaust port  46  to the left (i.e., to the side opposite to the central longitudinal section line  40  side). A slant angle θ 2  (not shown) of this slant is about 2° in the embodiment shown in FIGS. 3 and 5B but is generally preferably in the range of 0.5° to 5° in practice and is more preferably in the range of 1° to 3°. 
     The chin region of the outer shell  11  (i.e., a region opposing the chin of the wearer) has a pair of left and right air supply/exhaust holes  111   a  and  111   b , as shown in FIGS. 1 and 3. The air supply/exhaust holes  111   a  and  111   b  are long substantially sideways but slant slightly upward from the central longitudinal section line  40  side to the opposite side (i.e., to the left and right outward). The air supply/exhaust holes  111   a  and  111   b  may be covered with dust net or the like when necessary. The halves of the air supply/exhaust holes  111   a  and  111   b  which are on the central longitudinal section line  40  side respectively oppose the left and right lower portions  56   a  and  56   b  of the air supply path forming member  53 . The halves (i.e., the other half) of the air supply/exhaust holes  111   a  and  111   b  which are on the sides opposite to the central longitudinal section line  40  side oppose the exhaust path recesses  93   a  and  93   b . The outer shell  11  has a notch  112  at its substantially central portion, which is notched from the upper end downward, as shown in FIG.  5 A. The notch  112  has a size substantially equal to the sum of the sizes of the projecting surface  73  of the air supply port forming member  55 , the inverted U-shaped projecting ridge  80  and upper opening  78   a.    
     To build the three types of chin ventilator constituent members (i.e., the air supply path forming member  53 , the shutter member  54  and the air supply port forming member  55 ) into the head protecting body  2 , the steps described in the following items (i) to (iv) may be sequentially performed. 
     (i) First, the shutter member  54  is attached to the air supply port forming member  55 . 
     To perform this attaching operation, the tap  89  of the shutter member  54  is inserted in the upper opening  78   a  of the air supply port forming member  55  from the inside toward the outside. After the waved spring  79  rides over the engaged projection  87  of the shutter member  54  from the inner side to the outer side by utilizing the elasticity of the projections  85  of the shutter member  54  and the waved spring  79  of the air supply port forming member  55 , the engaged projection  87  is abutted against the step  79   a  of the waved spring  79 . In this state, when the shutter member  54  is moved substantially horizontally with respect to the air supply port forming member  55 , its engaged projection  87  is fitted in the recess of the waved spring  79  and held in position at three positions, i.e., the central position and the left and right positions. The substantially horizontal movement of the shutter member  54  is regulated as the connecting portion  88  abuts against the left and right surfaces of the upper opening  78   a  of the air supply path forming member  53 . 
     (ii) The air supply port forming member  55  attached with the shutter member  54  is temporarily attached to the air supply path forming member  53 . 
     To perform this attaching operation, the engaged projections  68   a  and  68   b  of the air supply path forming member  53  are fitted in the engaging holes formed in the rear surfaces of the projections  76   b  and  76   c  of the air supply port forming member  55 . In this case, when necessary, the projections  76   b  and  76   c  or the peripheries of the engaging holes may be coated with an adhesive, so the engaged projections  68   a  and  68   b  and the engaging holes can be connected to each other comparatively reliably and firmly. Simultaneously, the upper projecting ridge  60   c  of the air supply path forming member  53  is relatively fitted in the groove of the bend  81  of the air supply port forming member  55 . 
     (iii) The air supply path forming member  53  attached with the shutter member  54  is attached to the inner surface of the chin region of the outer shell  11 . 
     To perform this attaching operation, as shown in FIG. 5A, attaching screws (not shown) may be inserted in a pair of left and right screw insertion holes  113 , formed on the outer shell  11 , from the outer surface to the inner surface, then in the pair of left and right screw insertion holes  72   a  and  72   b  of the air supply port forming member  55 , and may be screwed into the pair of left and right attaching bosses  58   a  and  58   b  of the air supply path forming member  53 . In this case, the projecting surface  73  and inverted U-shaped projecting ridge  80  of the air supply port forming member  55  are inserted in the notch  112  of the outer shell  11 , and the lower portion and tap  89  of the connecting portion  88  of the shutter member  54  project forward from the notch  112 . The member main body  71  (excluding the thin-walled portions  71   a ), the projecting ridge  74   a  and the hanging portion  77  of the air supply port forming member  55 , and the inverted U-shaped bend  60 , those sides of the pair of left and right bends  61   a  and  61   b , which are opposite to the central longitudinal section line  40  side, and lower ends of the left and right lower portions  56   a  and  56   b  (further including the entire or part of the upper ends of the guide plates  62   a  to  64   a  and  62   b  to  64   b  depending on the case) of the air supply path forming member  53  abut against the inner surface of the outer shell  11 . As shown in FIG. 3, the left and right lower portions  56   a  and  56   b  of the member main body  56  of the air supply path forming member  53  respectively oppose those halves of the pair of left and right air supply/exhaust holes  111   a  and  111   b , which are on the central longitudinal section line  40  side, of the outer shell  11 . 
     (iv) The outer surface of the impact-on-the-chin-and-cheek absorbing liner  23  is abutted against the inner surface of the outer shell  11  and attached to it with an adhesive or the like. 
     This attaching operation is performed such that the fitting projection  92  of the impact-on-the-chin-and-cheek absorbing liner  23  is fitted in the fitting opening  57  of the air supply path forming member  53 , as shown in FIG. 3, and such that the almost or substantially entire air supply path forming member  53  is relatively fitted in the front recess  45  of the impact absorbing liner  23 . As a result, as shown in FIG. 3, the pair of left and right exhaust path recesses  93   a  and  93   b  of the impact absorbing liner  23  respectively oppose those halves of the pair of left and right air supply/exhaust holes  111   a  and  111   b , which are opposite to the central longitudinal section line  40  side, of the outer shell  11 . In this case, as shown in FIGS. 1 and 2, a conventionally known breath guard  114  may be interposed between the outer surface (i.e., the front surface) of the impact-on-the-chin-and-cheek absorbing liner  23 , and the inner surfaces (i.e., rear surfaces) of the outer shell  11  and air supply path forming member  53 , thereby attaching the breath guard  114  to the head protecting body  2 . 
     Through the steps described in the above items (i) to (iv), the three types of chin ventilator constituent members  53  to  55  can be built in the head protecting body  2 . In the built-in state, the chin ventilator mechanism  51  has the chin air supply path  121  and the pair of left and right chin exhaust paths  122   a  and  122   b  (to be described later). 
     The chin air supply path  121  is sequentially comprised of 
     1) those halves of the pair of left and right air supply/exhaust holes  111   a  and  111   b,  which are on the central longitudinal section line  40  side, of the outer shell  11 , 
     2) a pair of left and right (i.e., two) gaps defined by the outer surfaces of the left and right lower portions  56   a  and  56   b  of the air supply path forming member  53  and the inner surface of the outer shell  11  and including the lower portions of the straightening air supply paths  65   a  to  67   a  and  65   b  to  67   b,    
     3) one gap defined by the outer surface of the air supply path forming member  53 , the inner surface of the air supply port forming member  55  and the inner surface of the shutter member  54 , and including the upper portions of the straightening air supply paths  65   a  to  67   a  and  65   b  to  67   b , and 
     4) the notches  84  of the shutter member  54  and the notches  75  of the air supply port forming member  55  from its start point (i.e., the air inlet port to the chin air supply path  121 ) to its end point (i.e., the air outlet port from the chin air supply path  121 ). The start point of the chin air supply path  121  is formed by the outer surfaces of those halves of the pair of left and right air supply/exhaust holes  111   a  and  111   b , which are on the central longitudinal section line  40  side, of the outer shell  11 . These outer surfaces form the air inlet port to the chin air supply path  121 . The end point of the chin air supply path  121  is formed by the upper ends of the notches  75  of the air supply port forming member  55 . These upper ends form the air outlet port from the chin air supply path  121 . Hence, the chin air supply path  121  branches into two branches from the end point toward the start point. The three gaps described in the above items 2) and 3) respectively form air supply gaps. Accordingly, the three types of chin ventilator constituent members  53  to  55  and the chin region of the outer shell  11  make up the chin air supply path main body that occupies most of the chin air supply path  121 . The chin air supply path  121  is comprised of the chin air supply path main body and one halve of the air supply/exhaust hole  111   a  described in the item 1). 
     When the wearer wearing the full-face-type helmet  1  drives a motor cycle, outer air (i.e., external air) flows relatively from the substantially front surface into the air supply/exhaust holes  111   a  and  111   b  described in the item 1). Hence, those halves of the air supply/exhaust holes  111   a  and  111   b , which are on the central longitudinal section line  40  side, serve as the air supply hole portions of the chin air supply path  121 . The external air flows from the notches  84  and  75  described in the item 4) to near the lower end of the inner surface of the shield plate  4  through the two gaps described in the item 2) and one gap described in the item  3) , as shown in FIGS. 2 and 3. Therefore, the external air can be introduced into the head protecting body  2  through the chin air supply path  121 . The external air is straightened by the straightening air supply paths  65   a  to  67   a  and  65   b  to  67   b  while it flows upward in the three gaps described in the items 2) and 3). The external air flowing to near the lower end of the inner surface of the shield plate  4  (i.e., above the substantially central portion of the impact-on-the-chin-and-cheek absorbing liner  23  and above the breath guard  114 ) shifts upward along the inner surface of the shield plate  4  to reach near the upper end of the inner surface of the shield plate  4 . As a result, the external air flow can effectively prevent the shield plate  4  from being fogged by the breath exhaled by the wearer. 
     The chin air supply path  121  can be blocked by operating the shutter member  54 . More specifically, when the engaged projection  87  of the shutter member  54  engages with the central one of the three engaging recesses of the waved spring  79 , the projections (i.e., the blocking portions)  85  of the shutter member  54  block the notches (i.e., air outlet ports)  75  of the air supply port forming member  55 . When the wearer holds the tap  89  of the shutter member  54  and moves the shutter member  54  to the left or right so the engaged projection  87  of the shutter member  54  engages with another engaging recess, other than the central one, of the waved spring  79 , the projections  85  of the shutter member  54  are displaced from the notches  75  of the air supply port forming member  55  to substantially overlie on the projections  76 . Hence, the air outlet ports  75  of the air supply port forming member  55  are opened. Therefore, when the wearer operates the shutter member  54  to engage the engaged projection  87  with the central engaging recess of the waved spring  79 , the chin air supply path  121  can be blocked so air supply through it can be stopped. 
     The pair of left and right chin exhaust paths  122   a  and  122   b  are symmetrical (i.e., axi-symmetrical) about the central longitudinal section line  40  shown in FIGS. 5A and 5B as the axis of symmetry. Hence, the left chin exhaust path  122   a  will be described in detail with reference to FIGS. 3,  4 ,  5 A and  5 B, and a detailed description on the right chin exhaust path  122   b  will be omitted. 
     The left chin exhaust path  122   a  is sequentially comprised of 
     1) the exhaust port  46  of the left half of the impact-on-the-chin-and-cheek absorbing liner  23 , 
     2) the space surrounded by the upper, lower and rear surfaces  101 ,  102  and  103  of the exhaust path recess  93   a  of the left half of the impact-on-the-chin-and-cheek absorbing liner  23  and the defecting/partitioning plate  95   a  of the left half of the air supply path forming member  53 , and 
     3) that half (i.e., the other half) of the air supply/exhaust hole  111   a , which is opposite to the central longitudinal section line  40  side, of the outer shell  11   
     from its start point (i.e., the air inlet port to the chin exhaust path  122   a ) to its end point (i.e., the air outlet port from the chin exhaust path  122   a ). The start point of the left chin exhaust path  122   a  is formed by the inner surface of the exhaust port  46  of the left half of the impact absorbing liner  23 . This inner surface forms the air inlet port to the left chin exhaust path  122   a . The end point of the left chin exhaust path  122   a  is formed of the outer surface of that half of the air supply/exhaust hole  111   a , which is opposite to the central longitudinal section line  40  side, of the outer shell  11 . This outer surface forms the air outlet port from the left exhaust path  122   a . The space described in the item 2) forms an exhaust gap. 
     When the wearer wearing the full-face-type helmet  1  drives a motor cycle, as described above, the external air flows relatively from the substantially front surface into the other half of the air supply/exhaust hole  111   a  described in the item 3). Simultaneously, the external air abutting against near the central portion of the chin region of the outer surface of the outer shell  11  is deflected horizontally outward (i.e., from the central longitudinal section line  40  side to the left opposite to it) along the outer surface of the outer shell  11 , and flows backward. In this case, the external air flowing relatively from the substantially front surface into the other half of the air supply/exhaust hole  111   a  described in the item 3) is blocked by the front surface  103  of the exhaust path recess  93   a  in the left half of the impact-on-the-chin-and-cheek absorbing liner  23  (in this case, the slant angle θ 1  of this front surface  103  functions or a negative pressure is produced as will be described later), and is deflected horizontally outward. Also, of the external air deflected horizontally outward along the outer surface of the outer shell  11 , external air flowing to that half of the air supply/exhaust hole  111   a  described in item 3), which is on the central longitudinal section line  40  side, is deflected horizontally outward by the deflecting plate  95   a  described in the item 2), as shown in FIG.  3 . Hence, this external air flows out from that half of the air supply/exhaust hole  111   a  described in the item 3), which is on the central longitudinal section line  40  side, and flows away horizontally outward in front of the other half of the air supply/exhaust hole  111   a  along the outer surface of the outer shell  11 . This produces the negative pressure near the outer end of the exhaust path recess  93   a  and near the other half of the air supply/exhaust hole  111   a  described in the item 3). 
     Air in the impact-on-the-chin-and-cheek absorbing liner  23 , below the breath guard  114  and near the exhaust hole  46  described in the item 1) (i.e., internal air including breath exhaled by the wearer and near the intermediate position in the vertical direction of the chin region of the impact absorbing liner  23 ) flows into this exhaust hole  46 , reaches the other half of the air supply/exhaust hole  111   a  described in the item 3) through the space described in the item 2), and flows out of the outer shell  11  from this other half. Hence, that half of the air supply/exhaust hole  111   a , which is opposite to the central longitudinal section line  40  side, serves as the exhaust hole portion of the chin exhaust path  122   a . Since air in the head protecting body  2  can be exhausted to the outside through the chin exhaust path  122   a , the shield plate  4  can be prevented further effectively from being fogged by the breath exhaled by the wearer or the like. 
     (3) Description on Head Ventilator Mechanism  52   
     As shown in FIGS. 2 and 6, the head ventilator mechanism  52  has one or a plurality of (in the embodiment shown in FIGS. 2 and 6, a pair of left and right) ventilation grooves  131  extending substantially semicircularly from the front end to the rear end (in other words, from the front head region to the nape region through the top head region and back head region) through the substantially central portion, in the right-to-left direction, of the inner surface (i.e., inner circumferential surface) of the impact-on-the-head absorbing liner  21 . The ventilation grooves  131  serve as head air paths, and are wide from their start points to near the front head region and narrow from there to the top head region. The head ventilator mechanism  52  has the backing cover  22  covering almost or substantially the entire inner surface of the impact-on-the-head absorbing liner  21 , as described above. The backing cover  22  has a large number of ventilation openings  141 . The ventilation openings  141  serve as air supply openings or exhaust openings depending on their positions or how the helmet is used (i.e., the open/closed states of shutter members  143  and  145  to be described later). The head ventilator mechanism  52  is comprised of a forehead ventilator portion  132 , front head ventilator portion  133 , back head ventilator portion  134  and nape ventilator portion  135  respectively formed along the ventilation grooves  131 . Hence, in the following description, the forehead ventilator portion  132 , front head ventilator portion  133 , back head ventilator portion  134  and nape ventilator portion  135  will be described in separate items with reference to FIGS. 2 and 6. 
     (i) Description on Forehead Ventilator Portion  132   
     As described above, the forehead ventilator portion  132  has the ventilation openings  31  formed in the front-side engaged member  25  of the backing cover  22  and the ventilation openings  32  formed in the front-side engaged member  27  of the impact-on-the-head absorbing liner  21 . The ventilation openings  31  are continuous to the ventilation grooves  131  through the ventilation openings  32 . 
     Hence, as described above, the external air introduced into the head protecting body  2  through the chin air supply path  121  and reaching near the upper end of the inner surface of the shield plate  4  flows into the ventilation grooves  131  through the ventilation openings  31  and  32 , and flows toward the front head ventilator portion  133  through the ventilation grooves  131 . 
     (ii) Description on Front Head Ventilator Portion  133   
     The front head ventilator portion  133  has a pair of left and right air supply hole forming members  142  attached to the outer shell  11 , and the shutter members  143  respectively attached to the air supply hole forming members  142 . Thus, the pairs of left and right air supply hole forming members  142  and shutter members  143  correspond to the pair of left and right air supply/exhaust holes  111   a  and  111   b  in items of design, as shown in FIG.  1 . The front head regions of the outer shell  11  and the impact-on-the-head absorbing liner  21  respectively have air supply holes. The air supply holes formed in the outer shell  11  fit on cylindrical air supply hole portions  142   a  of the air supply hole forming members  142 . The air supply holes formed in the front head region of the impact-on-the-head absorbing liner  21  are continuous to the ventilation grooves  131 , and oppose the ventilation openings  141  formed in the backing cover  22  through the ventilation grooves  131 . Also, the shutter members  143  are slidably attached to the air supply hole forming members  142  such that they can selectively open and close the outer ends of the air supply hole portions  142   a  of the air supply hole forming members  142 . 
     When the shutter members  143  are open, the first air flow flowing through the ventilation grooves  131  from the forehead region toward the front head region of the head protecting body  2  merges with the second air flow flowing from the outside into the ventilation grooves  131  through the air supply hole portions  142   a . When the shutter members  143  are closed, the first air flow further flows as a single flow toward the back head region through the ventilation grooves  131 . When the first and second air flows merge, part of the merged air (mainly the second air flow portion) flows into the interior of the head protecting body  2  near the front head region through the ventilation openings  141  of the backing cover  22 . 
     (iii) Description on Back Head Ventilator Portion  134   
     The back head ventilator portion  134  has a pair of left and right exhaust hole forming members  144  attached to the outer shell  11 , and the shutter members  145  respectively attached to the exhaust hole forming members  144 . Thus, the pairs of left and right exhaust hole forming members  144  and shutter members  145  correspond to the pairs of left and right air supply hole forming members  142  and shutter members  143 , and air supply/exhaust holes  111   a  and  111   b  in terms of design, as shown in FIG.  1 . This makes the outer shell  11  look simple. The back head regions of the outer shell  11  and impact-on-the-head absorbing liner  21  respectively have exhaust holes. The exhaust holes formed in the outer shell  11  fit on cylindrical exhaust holes  144   a  of the exhaust hole forming members  144 . The exhaust holes formed in the back head region of the impact-on-the-head absorbing liner  21  are continuous to the ventilation grooves  131 , and oppose the ventilation openings  141  formed in the backing cover  22  through the ventilation grooves  131 . Also, the shutter members  145  are slidably attached to the exhaust hole forming members  144  such that they can selectively open and close the outer ends of the exhaust holes  144   a  of the exhaust hole forming members  144 . 
     When the shutter members  145  are open, the first air flow flowing through the ventilation grooves  131  from the front head region toward the back head region of the head protecting body  2  slightly merges with the second air flow flowing out from the inside of the backing cover  22  through the ventilation grooves  131  and exhaust holes  144   a . When the shutter members  145  are closed, the first air flow further flows substantially entirely toward the back head region through the ventilation ridge grooves  131 . 
     (iv) Description on Nape Ventilator Portion  135   
     The nape ventilator portion  135  is shown in enlargement in FIG.  6 . Referring to FIG. 6, the main body portion of the backing cover  22  is formed of porous nonwoven fabric  147  to which appropriate-shaped elastic blocks  146  made of a flexible elastic material such as urethane foam or another synthetic resin are attached with an adhesive or the like. The rear-side engaged member  26  is attached to the main body portion, which is on the elastic blocks  146  side, as described above. The ventilation openings  33  of the rear-side engaged member  26  are continuous to the ventilation grooves  131  through the ventilation openings  34  of the rear-side engaging member  28  of the impact-on-the-head absorbing liner  21 . 
     An exhaust port forming member  151  is attached to the lower end face of the rear portion of the impact-on-the-head absorbing liner  21  with a tape, adhesive, or the like. The exhaust port forming member  151  is comprised of a base plate portion  151   a  which forms the lower end face of the rear portion of the head protecting body  2 , and a pair of left and right exhaust ports  151   b  formed by expanding part of a pair of left and right portions of the base plate portion  151   a  like bags such that their longitudinal sections form almost triangular shapes. Each exhaust port  151   b  has a large number of slit-like inner exhaust holes  152  formed in a wall portion in front of the exhaust port  151   b , and an outer exhaust hole  153  formed by boring the lower end of the exhaust port  151   b  entirely. The outer exhaust holes  153  are continuous to the ventilation grooves  131  through the inner exhaust holes  152 . Hence, the outer ends of the outer exhaust holes  153  form the end points (i.e., air outlet ports) of the ventilation grooves (i.e., head air paths)  131 . 
     The outer shell  11  has a narrow or constricted portion  11   a  in the outer surface of the nape region at its rear portion to extend substantially horizontally. In the embodiment shown in FIG. 6, the constricted portion  11   a  is narrowed or constricted forward by about 9 mm (about 10 mm from the lower end of the rear portion of the lower rim member  12 ), from the lower end of the rear portion of the outer shell  11 , on the center line in the right-to-left direction of the outer shell  11 . The radius of curvature of the constricted portion  11   a  on this center line is about 15 mm. For this reason, that portion of the outer shell  11  (and accordingly the lower rim member  12 ) which is near the lower end of its rear portion slants downward from above in the backward direction on the center line, as shown in FIG. 6. A slant angle θ 3  of this slant is about 30°. The constricted portion  11   a  is constricted the most on the center line of the rear portion of the outer shell  11 , and is constricted less forward along the left or right side. The constricted portion  11   a  has a length in the back-and-forth direction of as large as about 50 mm, and a length in the right-to-left direction of as large as about 16 cm. The impact-on-the-head absorbing liner  21  also has a narrow or constricted portion  21   a  in the same manner as the outer shell  11 . The constricted portion  21   a  is substantially in tight contact with the constricted portion  11   a  of the outer shell  11 . 
     Hence, the air flow flowing relatively along the rear portion of the outer surface of the outer shell  11  is deflected by the constricted portion  11   a  sharply backward, so a portion near under the outer exhaust holes  153  of the exhaust port forming member  151  becomes a negative pressure. Thus, the first air flow flowing through the ventilation grooves  131  toward the nape region, and the second air flow flowing from the interior of the head protecting body  2  into the ventilation grooves  131  through the large number of clearances of the porous nonwoven fabric  147 , the ventilation openings  33  of the rear-side engaged member  26 , and the ventilation openings  34  of the rear-side engaging member  28  flow out from the outer exhaust holes  153  effectively through the inner exhaust holes  152  of the exhaust port forming member  151 . Thus, the air flow in the ventilation grooves  131  can be improved by the nape ventilator portion  135 . 
     The constricted portion  11   a  generally preferably satisfies one or more of the conditions described in the following items 1) to 5) in practice: 
     1) the constricted portion  11   a  should be constricted forward by 4 mm to 16 mm (more preferably by 6 mm to 12 mm) from the lower end of the rear portion of the outer shell  11 , or by 5 mm to 17 mm (more preferably by 7 mm to 13 mm) from the lower end of the rear portion of the lower rim member  12 , on the center line in the right-to-left direction of the outer shell  11 ; 
     2) the radius of curvature on this center line should be in the range of 6 mm to 25 mm (more preferably 10 mm to 20 mm); 
     3) that portion of the outer shell  11  or lower rim member  12  which is near the lower end of its rear portion should slant downward from above in the backward direction on the center line in the range of 20° to 40° (more preferably 25° to 35°) (in other words, the slant angle θ 3  should be in the range of 20° to 40° (more preferably 25° to 35°)); 
     4) the length in the back-and-forth direction should be in the range of 25 mm to 100 mm (more preferably 35 mm to 75 mm); and 
     5) the length in the right-to-left direction should be in the range of 8 cm to 32 cm (more preferably 12 cm to 24 cm). 
     Having described a specific preferred embodiment of this invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to that precise embodiment, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims. 
     In the above embodiment, the chin air supply path  121  of the chin ventilator mechanism  51  is comprised of the air supply/exhaust holes  111   a  and  111   b  of the outer shell  11  and three types of chin ventilator constituent members  53  to  55 , and the chin exhaust paths  122   a  and  122   b  of the chin ventilator mechanism  51  are comprised of the air supply/exhaust holes  111   a  and  111   b  of the outer shell  11 , the exhaust holes  46  and exhaust path recesses  93   a  and  93   b  of the impact-on-the-chin-and-cheek absorbing liner  23 , and the deflecting/partitioning plates  95   a  and  95   b  of the air supply path forming member  53 . Alternatively, the chin exhaust paths  122   a  and  122   b  may be comprised of, e.g., a separate pair of left and right tublar chin ventilator constituent members and air supply/exhaust holes  111   a  and  111   b  of the outer shell  11 . 
     In the above embodiment, the pair of left and right air supply/exhaust holes  111   a  and  111   b  are formed in the chin region of the outer shell  11 , and the center-side halves of the air supply/exhaust holes  111   a  and  111   b  form air supply hole portions while other halves thereof opposite to the center side form exhaust hole portions. However, the present invention does not necessary have this arrangement. For example, one air supply/exhaust hole may be formed at the substantial center in the right-to-left direction of the chin region of the outer shell  11 , the substantially central portion of this air supply/exhaust hole may be used as an air supply hole portion, and those portions of this supply/exhaust hole which correspond to the left and right sides of the air supply hole portion may be used as a pair of left and right exhaust hole portions. 
     In the above embodiment, the opening/closing shutter portion  83  of the shutter member  54  slides along the lower surface of the inner air supply port forming portion  74  of the air supply port forming member  55 . Alternatively, the opening/closing shutter portion  83  may slide along the upper surface of the inner air supply port forming portion  74 . 
     In the above embodiment, the ventilation grooves  131  with open loop-like longitudinal sections are formed in the inner surface of the head protecting body  2  in order to form head air paths. Alternatively, in place of the ventilation grooves  131  with the open loop-like longitudinal sections, closed loop-like elongated holes with circular longitudinal sections may be formed. In this case, the impact-on-the-head absorbing liner  21  may be halved into an outer liner portion on the outer shell  11  side and an inner liner portion opposite to the outer shell  11  side, and opposing grooves with open loop-like longitudinal sections may be formed in the inner surface of the outer liner portion and the outer surface of the inner liner portion. This pair of grooves can form elongated ventilation holes with closed loop-like longitudinal sections. 
     In the above embodiment, the present invention is applied to the chin ventilator mechanism  51 . The present invention can also be applied to other mechanisms or portions such as the front head ventilator portion  133  of the head ventilator mechanism  52 . 
     In the above embodiment, the present invention is applied to the full-face-type helmet  1 . Alternatively, the present invention can also be applied to helmets of other types, i.e., a jet- or semijet-type helmet, or a full-face-type helmet serving also as a jet-type helmet, the chin portion of which can be raised.