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BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ground drilling machine such as earth drilling (boring) machine for drilling a bore in earth for embedding, without open-cut operation to the earth, gas pipe, electric cable, signal cable sheath tube, fiber cable, water-supply pipe, sewer (sewage) pipe and the like, and a crawler drill for boring an earth to insert an explosive for blasting use, and also relates to a rod exchanger utilized for such ground drilling machine. 
     2. Prior Art 
     Prior art provides a crawler drill such as disclosed in Japanese Patent Laid-open Publication No. SHO 58-189493. 
     The crawler drill disclosed in this publication is equipped with a freely travelling vehicle body, a frame structure mounted to the vehicle body, a drilling unit movable along the frame structure, a rod having, at its front end, a drill bit and rotated and propelled by this drilling unit and a rod exchanger mounted to the frame structure. The rods are incorporated in the rod exchanger so that the rods are accommodated in turns to the drilling unit to sequentially drill the earth (ground). 
     This rod exchanger is provided with a main body into which a plurality of rods are accommodated and a rod exchanging unit or section mounted to the main body so as to carry the rods between the main body and the frame structure. The main body of the rod exchanger is mounted to the side surface of the frame structure. 
     Accordingly, in such crawler drill of the prior art, since the rod exchanger is cantilevered by the frame structure, a large load is applied to the frame structure, so that it is obliged to make the frame structure large and heavy. 
     Furthermore, in such crawler drill, a large bending load will be applied to the machine body of the rod exchanger, and particularly, a large load will be applied to a portion of the machine body which is mounted to the frame structure. Therefore, it becomes necessary to make the strength of that portion large so as to allow an entire weight of the rod exchanger to be supported, thus making the size and weight of the rod exchanger large and heavy, being disadvantageous. 
     As mentioned above, large size and heavy weight of the frame structure and the rod exchanger result in large load acting on the vehicle body of the crawler drill, and hence, the vehicle body itself is made large and heavy. 
     Such defects bring the entire structure of the crawler drill having a large size and heavy weight, and hence, it is difficult to carry out the drilling working by the crawler drill set at a narrow site or portion. The entire height (from the ground surface) of the crawler drill is high, preventing worker&#39;s visibility, and moreover, it is difficult for the worker to exchange the rods and carry out the rod propelling operation and, moreover, any safe operation cannot be expected because of high position of the gravity center of the crawler drill. 
     The body of the rod exchanger is formed with a plurality of rod accommodation (receiving) recesses arranged along a circular locus thereof. The rod exchanging unit is composed of a swingable arm and a pair of claws provided, to be opened or closed, at the front end portion of the arm. A rod accommodated in the recess formed to the rod exchanger body is grasped by the paired claws, and the arm is swung and carried to the frame. When reached to the frame, the rod is released from the claws and the rod is then connected to the drilling unit. According to the manner reverse to that mentioned above, the rod is accommodated in the recess of the rod exchanger body. 
     In order to carry out the aforementioned operation, it is necessary to secure a large space for the swing motion of the claws in opposite sides of the rod diametral direction at the time when the rod received in the rod accommodation recess is grasped. Therefore, the fact that the large space is required leads to a defect that it is necessary to increase a distance between adjacent two rods accommodated in the recesses of the rod exchanger body, and hence, the number of the rods to be accommodated is reduced. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a ground drilling machine capable of making a frame structure light and compact and a rod exchanger utilized therefor capable of accommodating a lot of rods without increasing an arrangement or location space. 
     This and other objects can be achieved according to the present invention by providing a ground drilling machine comprising: 
     a machine body; 
     a rod propelling device having a frame structure mounted to the machine body; 
     a rod exchanging device mounted to the frame structure of the rod propelling device; and 
     a support unit provided for the machine body for supporting the rod exchanging device. 
     According to this structure, since the rod exchanging device is supported by the machine body, a load to be applied to the frame structure of the rod propelling device can be reduced, so that the frame structure can be made light and compact. 
     Furthermore, since a large bending load is not applied to the main body portion of the rod exchanging device, the rod exchanging device itself can be made light and compact. Particularly, any large load is not applied to the portion through which the rod exchanging device is mounted to the frame structure, so that this portion can be especially made light and compact. 
     As mentioned above, the frame structure, the rod exchanging device and the portion through which the rod exchanging device is mounted to the frame structure are all made light and compact, so that the load to be applied to the machine body can be reduced, thus making the machine body compact and light, resulting in the realization of the light and compact entire structure of the ground drilling machine. 
     Accordingly, the ground drilling machine having a large working capacity can be installed in a narrow working site such as on a sidewalk or a narrow path, thus improving a working efficiency. 
     Moreover, since the total height of the ground drilling machine can be made low, the visibility of an operator can be improved and the rod exchanging working and rod propelling working can be performed smoothly. Also, the ground drilling machine can have a low center of gravity to be stable. 
     In a preferred embodiment of the above aspect, the frame structure is movably mounted to the machine body and also the rod exchanging device is movably supported by the support unit also. 
     According to this structure, the rod exchanging device is moved together with the frame structure, so that the rod propelling device can be easily set to an aimed ground position. Moreover, since the positional relationship between the frame structure and the rod exchanging device is always constant, the rod exchanging working can be done regardless of the position of the frame structure. 
     Furthermore, the frame structure and the rod exchanging device can be simultaneously moved with respect to the machine body and the support portion of the machine body, respectively, the width of the moving contact portions thereof can be made large, so that the movement thereof can be stably performed and the machine body can be easily and accurately set to the aimed position with less swing motion thereof. 
     Furthermore, according to the present invention, there is also provided a rod exchanging device, particularly for the ground drilling machine of the aspect mentioned above, comprising: 
     a main body portion; 
     a rod accommodation portion mounted to the main body portion for accommodating a plurality of rods with a space from each other; and 
     a rod exchanging unit provided with a rod grasping device having a grasping portion which is movable between a position inside the main body portion and a position outside the main body portion, the grasping portion being formed with a fixed portion and a movable portion. 
     According to this structure, the rod can be grasped by both the fixed portion and the movable portion even in a presence of a small space capable of one movable portion being moved near the rod accommodated in the rod accommodation portion, and therefore, the space between the adjacent rods accommodated in the rod accommodation portion can be made small and, hence, a lot of rods can be accommodated. 
     The rod accommodation portion may provide a disc shaped structure adapted to accommodate a plurality of rods along the circular locus thereof with a space from each other and to be rotatable. 
     According to this structure, rod accommodation portion can be made rotatable which requires less space for accommodation, thus providing a light and compact rod exchanging device. 
     The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a right side view showing one embodiment of a ground drilling machine according to the present invention; 
     FIG. 2 is a front view of the ground drilling machine of FIG. 1; 
     FIG. 3 is a plan view of the ground drilling machine of FIG. 1; 
     FIG. 4 is a left side view of the ground drilling machine of FIG. 1; 
     FIG. 5 is a schematic plan view of a support portion (structure) of the ground drilling machine of FIG. 1; 
     FIG. 6 is a left side view of the support structure of FIG. 5; 
     FIG. 7 is an enlarged sectional view taken along the line VII—VII in FIG. 4; 
     FIG. 8 is an enlarged sectional view taken along the line VIII—VIII in FIG. 4; 
     FIG. 9 is a plan view, in an enlarged scale, of a section including a rod wrench and a rod damper of the ground drilling machine of FIG. 1; 
     FIG. 10 is a front view, in an enlarged scale, of a section including the rod wrench and the rod clamper of FIG. 9; 
     FIG. 11 is a sectional view taken along the line XI—XI in FIG. 9; 
     FIG. 12 is a sectional view taken along the line XII—XII in FIG. 9; 
     FIG. 13 is a sectional view taken along the line XIII—XIII in FIG. 9; 
     FIG. 14 is a right side view showing one example of a rod exchanger of the ground drilling machine of FIG. 1; 
     FIG. 15 is a front view of the rod exchanger of FIG. 14; 
     FIG. 16 is a back view of the rod exchanger of FIG. 14; 
     FIG. 17 is a sectional view taken along the line XVII—XVII in FIG. 14; 
     FIG. 18 is a sectional view taken along the line XVIII—XVIII in FIG. 14; 
     FIG. 19 is a sectional view taken along the line XIX—XIX in FIG. 14; 
     FIG. 20 is a right side view, in an enlarged scale, of a rod grasping device of the rod exchanger of FIG. 14; 
     FIG. 21 is an enlarged front view of the rod grasping device of FIG. 20; and 
     FIG. 22 is a front view of another example of a rod exchanger of the ground drilling machine of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     One preferred embodiment of the present invention will be described hereunder with reference to the accompanying drawings. 
     First, with reference to FIGS. 1 to  3 , a ground drilling machine of the present invention has a machine body  1  to which a pair of travelling bodies  2  are mounted at its both lateral side portions. Each of these travelling bodies  2  are of crawler type structure, but may be composed of wheel type structure. The machine body  1  may be formed as self-propelled type or portable type. 
     A rod propelling device  3  is mounted to a central position in the width direction of the machine body  1 , i.e., central portion between the paired travelling bodies  2 , to be movable in forward and rearward (longitudinal) direction in an inclined manner such that the front side portion thereof is positioned to be lower than the rear side portion with respect to a horizontal plane. 
     The rod propelling device  3  is provided with a frame  4 , which may be called hereunder as frame structure  4 , a cradle  5  reciprocally movable along the longitudinal direction of the frame  4 , a motor  6  for rotating a rod mounted to the cradle  5 , an anchor fixing portion  7  mounted to a front lower portion of the frame  4 , a rod wrench  8  mounted to a front upper portion of the frame  4 , a rod damper  9 , and a rod propelling motor  10  disposed to a rear portion of the frame  4 . Thus, the rod propelling device  3  is provided with a mechanism for reciprocally moving the cradle  5 . 
     This mechanism for reciprocally moving the cradle  5  is provided with a driving (drive) sprocket  11  mounted to a rear portion of the frame  4 , a driven sprocket  12  mounted to a front portion of the frame and a chain stretched around these driving and driven sprockets  11  and  12 . 
     The driving sprocket  11  is rotated in a reversible manner by means of rod propelling motor  10 , and the chain  13  is connected to the cradle  5 . According to such structure, when the driving sprocket  11  is normally rotated by the rod propelling motor  10 , the cradle  5  is moved forward and then when rotated reversibly, the cradle  5  is moved rearward, thus performing the reciprocal motion. 
     As shown in FIGS. 1 and 4, the machine body  1  is provided with a support portion (structure)  14  for supporting the frame structure  4  of the rod propelling device  3  in an inclined attitude. The support structure  14  is provided, as shown in FIGS. 5 and 6, with a plurality of vertical plates  15  and horizontal plates  16 , the latter being inclined so that the front side portion thereof is lower than the rear side portion with respect to the horizontal plane. 
     A slide surface plate  17  and a lateral pair of side surface guide pieces  18  are disposed to each of front and rear end portions of the horizontal plate  16 . The slide surface plate  17  is formed of a material having a small friction coefficient. 
     Referring to FIG. 7, the frame  4  has a lower surface  4   a , as viewed, which is rested on the slide surface plate  17  so that the frame  4  is supported by the support structure  14  to be movable in the longitudinal direction thereof. Protruded members  4   c  are formed on lateral side surfaces of the frame  4  so as to be contacted to lower surfaces of the side surface guide pieces  18  to thereby prevent the frame  4  from raising. 
     A cylinder (or cylinder assembly)  19  for movement is disposed, for example, as shown in FIG. 1, between the front side portion of the machine body  1  and the rear side portion of the frame  4 . 
     When this cylinder  19  is operated to be expanded, the frame  4  is moved rearward, then, the anchor fixing portion  7  is separated from the ground surface, and the rod propelling device  3  takes its non-working position (machine body travelable position) such as shown in FIG.  1 . 
     On the contrary, when the cylinder  19  is operated to be contracted, the frame is moved forward, then, the anchor fixing portion  7  is contacted to the ground surface, and the rod propelling device  3  takes its working position. 
     Further, the machine body  1  is provided, at its front one side portion, with an operator&#39;s seat  20 , a working machine lever  21 , a travelling lever  22 , a control board  23  and so on as shown in FIG.  1  and FIG.  3 . 
     With reference to FIG. 3, the operator&#39;s seat  20 , the travelling lever  22  and the control board  23  are disposed to be movable between a projected position projected from a lateral one side surface of the machine body  1  and an accommodation position having the surface position substantially flash with the above-mentioned lateral one side surface of the machine body  1 . 
     A lateral pair of outriggers  24  are mounted to lateral side portions of the rear end portion of the machine body  1 . 
     Further, a rod exchanger (rod exchanging device)  30  is mounted to a portion of the frame  4  opposing to the operator&#39;s seat  20 . 
     The rod exchanger  30  is provided with a body portion  31  into which a plurality of rods are detachably accommodated and a rod exchanging portion  32  at which the rod is received from or transported to the frame  4 . The body portion  31  is detachably mounted to the side surface of the frame  4 . 
     As shown in FIGS. 4,  5  and  6 , a support portion (structure)  33  for supporting the rod exchanger  30  is formed to the vertical plate  15  of the machine body  1 . The support structure  33  has an upper surface  34  inclining in the same direction and at substantially the same angle as those for the horizontal plate  16 , and slide surface plates  35  are attached to the front and rear end side portions of the upper surface  34  of the support structure  33 . 
     A slide (slidable) frame  36  is mounted to an entire surface of the lower portion of the body portion  31  of the rod exchanger  30 , and this slide frame  36  is rested on a slide surface plate  35 , as shown in FIG. 7, so that the body portion  31  is supported by the support structure  33  to be movable in the longitudinal (i.e., forward and rearward) direction. One of these support structure  33  and slide frame  36  may be composed of a roller member. 
     According to the structure mentioned above, the rod exchanger  30  is supported by the support structure  33  of the machine body  1  through the slide frame  36  to be movable in the longitudinal direction along the support structure  33  together with the frame structure  4  of the rod propelling device  3 . 
     The respective members or structures mentioned above will be described hereunder more concretely. 
     With reference to FIGS. 4 and 8, the rod rotating motor  6  and a reduction mechanism  40  are fixed to an upright (standing) portion  5   a  of the cradle  5 , and an output side of the rod rotating motor  6  is coupled to a rotation shaft  41  through the reduction mechanism  40 , and the front end portion of the rotation shaft  41  is formed as a screw portion  41   a.    
     The cradle  5  clamps a lateral pair of guide plates  42  fixed to the upper surface  4   a  of the frame  4  in a slidable manner to be reciprocally movable along the guide plates  42 . 
     A hose receive member  43  is mounted to a side surface  4   b  of frame  4  on the side of the operator&#39;s seat  20 . 
     As shown in FIG. 3, the output side of the rod propelling motor  10  is operatively connected to the driving sprocket  11 . 
     Furthermore, the rod wrench  8  and the rod damper  9  have substantially the same structure except that the former has a cylinder  59  and the latter instead has a link  60 , the cylinder  59  and the link  60  being mentioned hereunder, and as shown in FIGS. 9 and 10, each of the wrench  8  and rod clamper  9  has a structure that a box-shaped body  52 , having an upper opening in cross section, is mounted to be vertically swingable with a pair of hollow pins  53  to a set of brackets  51  of a plate  50  attached to the upper surface  4   d  of the frame  4 , and a rod grasping member  54  is mounted to the body portion  52 . 
     The rod grasping member  54  is provided, as shown in FIG. 9, with a pair of side plates  56  attached, through pin-slot connection, to the body portion  52  to be movable by a predetermined stroke, a stationary grasping portion  55  fixed to the side plates  56 , a movable grasping portion  57  movable along the paired side plates  56  and a cylinder (cylinder assembly)  58  attached to the side plates  56  so as to move the movable grasping portion  57 . 
     The stationary grasping portion  55  and the movable grasping portion  57  are formed detachably, as shown in FIG. 11, with grasping pieces  55   a  and  57   a , each having a V-shaped section, so as to grasp the rod between these V-shaped portions of the grasping pieces  55   a  and  57   a . The movable grasping portion  57  has a lower portion to which a movable grasp guide  57   b  is attached. The movable grasping portion  57  projects on the side of the stationary grasping portion  55  over the grasping piece  57   a.    
     The rod can be inserted into the portion between the stationary grasping portion  55  and the movable grasping portion  57  through a hollow portion  53   a  of the hollow pin  53 . 
     FIGS. 9 and 10 show a release state in which the grasping state is released and the stationary grasping portion  55  and the movable grasping portion  57  are spaced, and in this state, the respective grasping pieces  55   a  and  57   a  are spaced by a distance through which the rod can be inserted. 
     In the rod inserted state, when the cylinder  58  is expanded, the movable grasping portion  57  is moved, together with a piston rod  58  of the cylinder  58 , towards the stationary grasping portion  55  till the grasping piece  57   a of the movable grasping portion  57  abuts against the rod. 
     Thereafter, when the cylinder  58  is further expanded, a cylinder tube  58   b  is moved, together with the side plates  56 , in a direction reverse to that mentioned above with respect to the piston rod  58   a  because the movable grasping portion  57  now abutting against the rod is not moved further, and as a result, the stationary grasping portion  55  is moved, together with the side plates  56 , towards the movable grasping portion  57  and, then, the grasping piece  55   a  abuts against the rod. 
     In this manner, the rod is grasped, i.e., clamped, by the grasping pieces  55   a  and  57   a  of the stationary and movable grasping portions  55  and  57 , respectively. 
     On the contrary, when the cylinder  58  is contacted in the state mentioned above, the respective members and portions mentioned above are moved or operated in the manner reverse to that mentioned above so as to take a grasping release state shown in FIG. 8 or  9 . 
     With reference to FIG. 12, a cylinder  59  is connected with the body portion  52  of the rod wrench  80  and the frame  4  between them, and when this cylinder  59  is expanded or contracted, the rod wrench  8  is vertically swung in the shown state. The plate  50  is formed with a hole  50   a  so that the side plates  56  do not interfere with the plate  50  at the time when the rod wrench  8  is swung upward. 
     Referring to FIG. 10, a link  60  is connected with the body portion  52  of the rod damper  9  and the frame structure  4  between them so as to fix the rod damper  9  at substantially a horizontal attitude in the shown state. 
     Further, as shown in FIG. 13, the hollow portions  53   a of the above-mentioned tow-paired hollow pins  53  are arranged to be substantially coaxial so as to provide a state that the rods  62  and  63  can be continuously inserted into the rod grasping portion  54  of the rod wrench  8  and the rod grasping portion  54  of the rod damper  9 . 
     The plate  50  is mounted with a receiving plate  61  so that the rods can be smoothly inserted into the hollow portions  53  of the hollow pins  53 , respectively. 
     According to the structures mentioned above, as shown in FIG. 13, the preceding rod  62 , for example, the rod  62  having a drill head having an inclined surface at the front end portion thereof and propelled into the ground, is grasped (clamped) by the stationary grasping portion  55  and the movable grasping portion  57  of the rod damper  9 , and then, a male screw portion  63   a  of a succeeding rod  63  connected to the rotation shaft  41  rotated by the motor  6  and propelled by the cradle  5  is forced against a female screw portion  62   a  of the preceding rod  62  to be screwed therein. Thus, the succeeding rod  63  is connected with the preceding rod  62 . 
     The disconnection of the succeeding rod  63  from the preceding rod  62  is performed as follows. The preceding rod  62  and the succeeding rod  63  can be unscrewed by grasping the preceding rod  62  and the succeeding rod  63  by the rod damper  9  and the rod wrench  8 , respectively and expanding the cylinder  59  so as to swing upward the rod wrench  8 . In succeeding, the succeeding rod  63  is released from the grasp by the rod wrench  8  and rotated by the cradle  5  in the unscrewing direction, so that the succeeding rod  63  is separated from the preceding rod  62 . 
     Next, the concrete structure or shape of the rod exchanger (rod exchanging device)  30  will be described. Further, although the rod exchanger  30  is mounted to the machine body  1  in a manner inclining with respect to a horizontal plane, this matter will be explained with showing the rod exchanger in a horizontal state. 
     With reference to FIGS. 14,  15  and  16 , a front side plate  70  (lower side plate in an inclining direction) and a rear side plate  71  (upper side plate in the inclining direction), both having approximately rectangular shape, are coupled with an interval by means of a plurality of coupling members in the shape of rods  72 . 
     A rotation shaft  73  is also supported to be rotatable between the front and rear side plates  70  and  71 , and a plurality of rod accommodation plates  74  are mounted to this rotation shaft  73  with intervals in the longitudinal direction thereof. Each of the rod accommodation plates  74  has a disc shape, as shown in FIG. 17, and is formed with a plurality of rod receiving recesses  74   a  at its outer periphery with intervals along the circumferential direction thereof. 
     A rod support plate  74   b  is attached to the most front side (right side end portion as viewed in FIG. 14, for example) of the rotation shaft  73 . This rod support plate  74   b  has a disc shape and contacts a plurality of balls  70   a  arranged to the front side plate  70  and then supports the rods so as not to be moved in the longitudinal direction. The respective rod accommodation plates  74 , each having the structure mentioned above, are rotated together with the rotation shaft  73  which is driven by means of motor  75 . 
     According to the structure mentioned above, a rod accommodation unit (section) X is constituted by the rotation shaft  73 , the plural rod accommodation plates  74  and the rod support plate  74   b , and such rod accommodation unit X is rotatable and receives a plurality of rods with spaces along the circular locus. 
     A pair of rod coming-off prevention plates  76  are arranged to both end sides in the longitudinal direction of the coupling rods  72 . 
     This rod coming-off prevention plate  76  is formed, as shown in FIG. 17, with a substantially circular guide hole  77  concentrical with the rotation shaft  73 , and a ring-shaped space is formed between the guide hole  77  and the outer peripheral portion of the rod accommodation plate  74 . 
     A rod  78  accommodated in the recess  74   a  of the rod accommodation plate  74  contacts the guide hole  77  so that the rod  78  is not come off at the time when the rod accommodation plate  74  is rotated together with the rotation shaft  73 . 
     The rod coming-off prevention plate  76  is formed, on its frame side portion, with a cutout opening  79  for transferring the rod. This cutout opening  79  has a dimension, in its rotational direction, larger by a diameter of one rod. A link  80  is attached, to be vertically swingable, to an upper edge portion of the cutout opening  79  and a press piece  81  is attached to this link  80  to be swingable. A pin  80   a  secured to the link  80  is fitted into an arcuate groove  81   a  formed to the press piece  81  to thereby limit or restrict the swingable range of the press piece  81  with respect to the link  80 . 
     Thus, as mentioned above, this press piece  81  acts to prevent the coming-off of the rod from the cutout opening  79  at the rotating time. At the rod taking-out time, the press piece  81  together with the link  80  is swung by the rod  78 , and at the rod accommodating time, the press piece  81  is swung inward with respect to the link  80  along the pin  80   a.    
     The aforementioned slide frame  36  is arranged throughout the lower portions of the front side plate  70 , the rear side plate  71  and the rod coming-off prevention plate  76  as best shown in FIG. 14, for example. 
     According to the structure mentioned above, the body portion  31  of the rod exchanger  30 , having a rod accommodating portion which accommodates a plurality of rods along the circular locus with spaces and is rotatable, is formed. 
     Furthermore, with reference to FIGS. 15 and 16, a pair of transverse mounting members  82  are fastened by means of bolts to both end side portions in the longitudinal direction of the opposite side surface  4   b  to the operator&#39;s seat  20 , of the frame structure  4  of the rod propelling device  3 . 
     Each of these transverse mounting members  82  is provided with a recessed portion  82   a  having an upward opening and each of the front and rear side plate  70  and  71  is provided with a circular lower mounting projection  83  at a portion lower than the rotation shaft  73  of the front and rear side plates  70  and  71 . The lower mounting projection  83  is fitted into the upward recessed portion  82   a  and then fixed, to be detachable, to the transverse mounting member  82  by screwing a locking screw  84  throughout the lower mounting projection  83 . 
     Vertical mounting members  85  are secured to the transverse mounting members  82 , respectively, to thereby constitute a mounting structure. 
     A bracket  86  formed with recessed portions  86   a  opened upward is fixed to each of the vertical mounting members  85  to a position above the rotation shaft  73 . Furthermore, circular upper mounting projections  87  are formed to the front side plate  70  and the rear side plate  71 , respectively, and the upper mounting projections  87  are fitted into the upward recessed portions  86   a  formed to the bracket  86 . 
     Further with reference to FIGS. 14 and 18, a pair of rod members  88  are secured to intermediate portions in the longitudinal direction of the two connection rods  72  mounted to the upper side portions of the front and rear side plates  70  and  71 , and arms  89  are secured to the respective rod members  89  to be vertically swingable and laterally slidable. 
     Each of the respective arms  89  usually takes a tilted attitude contacting the connection rod  72  as shown in FIG. 14 with an image line, and at a time of removing the main body portion  31  of the rod exchanger  30 , takes an obliquely upward attitude as shown in FIG. 14 with a solid line so as to be lifted upward by means of crane, for example, through a lifting rope  90  or like. 
     As mentioned above, by connecting the lifting rope  90  to the arm  89  and unscrewing the lateral locking screws  84 , the main body portion  31  of the rod exchanger  30  can be lifted up. Further, the motor  75  is mounted to the transverse mounting member  82  as shown in FIGS. 14 and 16, and a gear  75   a  driven by the motor  75  is meshed with a gear  73   a  mounted to the rotation shaft  73 , so that the gear  73   a  is moved upward together with the main body portion  31  to be thereby separated from the gear  75   a.    
     Further, the main body portion  31  of the rod exchanger  30  can be temporarily attached to the frame structure  4  by lowering the main body portion  31  of the lifted-up rod exchanger  30  and then fitting the upper and lower mounting projections  87  and  83  into the upward recessed portion  86   a  of the bracket  86  and the upward recessed portion  82   a  of the transverse mounting member  82 , respectively. 
     In this state, the main body portion  31  of the rod exchanger  30  can be attached to the frame structure  4  by screwing the locking screws  84 . 
     Thus, according to the manner mentioned above, the main body portion  31  of the rod exchanger  30  can be easily attached or detached. 
     Furthermore, a transverse connection member  91  is secured to the paired vertical mounting members  85  so as to extend therebetween. A pair of brackets  92  are mounted with a space to a surface of the transverse connection member  91  on the side of the frame  4 . 
     As shown in FIG. 19, a transverse shaft  93  is secured to each of these brackets  92 , and each of other brackets  94  is supported to each of these transverse shafts  93  to be swingable. A transverse member  95  is further connected between these brackets  94 , and this transverse member  95  is mounted to be swingable with respect to the transverse connection member  91 . 
     Furthermore, as shown in FIG. 18, a bracket  96  is fixed to a surface, opposite to the side of the frame  4 , of the longitudinally central portion of the transverse connection member  91 , and a cylinder  98  for the swing motion is connected between this bracket  96  and the bracket  97  fixed to the transverse member  95 . Further, a pair of rod grasping devices  100  are mounted to longitudinal both end portions of the transverse member  95 , respectively. 
     According to the manner mentioned above, a rod exchanging unit (section)  32  is constituted, which will be operated as follows. 
     The rod grasping devices  100  are swung between a position inside the main body portion  31  of the rod exchanger  30  as shown with the solid line in FIG. 19 and a position outside the main body portion  31  (i.e., frame side position) shown with an imaginary line upon the expansion and contraction of the cylinder  98 . 
     In an arrangement in which each of the rod grasping devices  100  is positioned in the main body portion  31  of the rod exchanger  30 , the grasping portion  101  projects inside the cutout opening  79  of the rod coming-off prevention plate  76 . 
     On the other hand, in the arrangement in which each of the rod grasping devices  100  is positioned to the frame side position mentioned hereinbefore, the grasping portion  101  accords with the center of the rotation shaft  41  rotated by means of the rod rotating motor  6 . 
     The concrete structure of the rod grasping device  100  will be described hereunder. 
     With reference to FIGS. 20 and 21, the rod grasping device  100  is provided with a body portion  104  which is formed by connecting lower portions of a pair of side plates  102  through a plate  103  with a space, and an upper portion of the body portion  104  is attached to the transverse member  95 . 
     The paired side plates  102  have lower end portions to which a fixed portion  105  is mounted. 
     A movable portion  106  is bent so as to provide substantially a crank-shaped structure, and a claw portion  106   a  is formed to the lower end portion thereof so as to direct transversely. The upper portion of the movable portion  106  is coupled via a pin  108 , to be swingably, to a cylinder  107  for grasping which is mounted to the upper portion of the body portion  104 . 
     Rollers  109  are mounted to both ends of the pin  108  so as to be slidably fitted into vertically elongated guide slots  110  formed to the paired side plates  102 , so that, upon the expansion or contraction of the grasping cylinder  107 , the pin  108 , i.e., upper portion of the movable claw  106 , is vertically linearly moved along the guide slot  110 . That is, rollers  109  and the guide slots  110  constitute a guide unit (section) for linearly moving the upper portion of the movable portion  106  (i.e., coupling portion between the grasping cylinder  107  and the movable portion  106 ). 
     Furthermore, rollers  111  are mounted to the paired side plates  102  at portions corresponding to intermediate portions in the longitudinal direction of the guide slots  110 . The movable portion  106  is urged upward by means of spring  112 , and an opposite side surface  106   b  to the claw portion  106   a , of the movable portion  106  contact to the rollers  111  for the movable portion  106  in a slidable manner. 
     Hereunder, rod grasping operation and releasing operation by means of the rod grasping devices will be described. 
     At the time when the grasping cylinder  107  is contracted, the movable portion  106  moves upward along the rollers  111  for the movable portion  106 , so that the movable portion  106  is swung downward against the urging force of the spring  112  and the claw portion  106   a  of the movable portion  106  takes the rod grasping position opposing to the fixed portion  105 . 
     When the grasping cylinder  107  is further contracted from the position mentioned above, the movable portion  106  moves linearly upward towards the fixed portion  105  to thereby take a position shown in FIG. 21 with the solid line, at which the rod is clamped, i.e., grasped, by the claw portion  106   a  and the fixed portion  105 . At this time, the claw portion  106   a  and the fixed portion  105  form the grasping unit (section) mentioned hereinbefore. 
     When the grasping cylinder  107  is expanded from the aforementioned state, the movable portion moves down and, then, is swung gradually upward by means of the spring  112  to thereby take the releasing position shown with the imaginary line in FIG.  21 . In this state, the claw portion  106   a  is apart from the fixed portion  105 . 
     As mentioned above, the movable portion  106  is swung between the grasping position opposing to the fixed portion  105  and the releasing position apart from the fixed portion, so that the grasping and releasing operation for the rod can be performed even with a small space in which the movable portion  106  can be swung therebetween. Accordingly, the circumferential intervals of the recessed portions  74   a  for receiving the rods of the rod accommodation plate  74  can be made small so as to receive the rods as many as possible. 
     For example, as shown in FIG. 19, according to the structure mentioned above, the fixed portion  105  is located above one rod  78 , and the movable portion  106  is swung with the state that the next rod receiving recess  74   a  receives no rod to thereby grasp the rod  78 . Accordingly, a lot of rods  78  can be accommodated. 
     FIG. 22 represents another example of the rod exchanger  30 , in which the main body portion  31  has a structure capable of accommodating the rods  78  in an superposed state in the vertical direction as viewed. 
     With reference to this example of the rod exchanger of FIG. 22, the rod exchanging section  32  is composed of a movable portion  122 , which is reciprocally movable by an associated operation of a pinion  120  and a rack  121  and a rod receiving member  123  mounted to the movable portion  122  to be swingable. According to this structure, the rod  78  accommodated in the main body portion is received on the rod receiving member  123  by moving the movable portion  122  and then moved to the frame structure  4  by moving the movable portion  122  towards the frame structure  4 . 
     Further, in this example, the main body portion  31  of the rod exchanger  30  is mounted to the frame structure  4 , and the slide frame  36  contacts the support portion  33  of the machine body  1  to thereby support the rod exchanger  30  by the machine body  1 . 
     Further, it is to be noted that, in the described embodiment, the present invention will be utilized as a ground drilling machine by propelling under the ground a rod provided with a leading portion having the inclined pressure receiving surface. It may be utilized as a crawler drill by utilizing a rod having a drill bit. 
     Furthermore, the frame structure may be arranged horizontally or to be vertically swingable in place of the inclined structure. The frame  4  may be fixed without being movable in the longitudinal direction thereof. 
     Still furthermore, it is further noted that, although the present invention is disclosed as an invention which is applicable to the ground drilling machine and the rod exchanger utilized therefor, the present invention is not limited to such specific embodiment or application, and many other applications will be suggested for those skilled in the art. Furthermore, it will be caused for experts in this art field to make various amendments, modifications and changes in the details of the illustrated and described embodiments so as to be conformed with design or like or with the necessity of the applications. Accordingly, it is reasonable that the present invention is understood by a method coincident with correct meaning or proper aspect of broader scopes of the appended claims.

Summary:
A ground drilling machine includes a machine body a rod propelling device, a rod exchanging device and a support unit provided for the machine body for supporting the rod exchanging device. The rod propelling device has a frame movably mounted to the machine body. The frame is slidable on a support portion provided for the machine body. The rod exchanging device is attached to the frame of the rod propelling device via a transverse mounting member. The rod exchanging device is also supported on the support unit so as to be slidable on the support unit along with the movement of the rod propelling device without changing of its relative position to the rod propelling device. The rod exchanging device can be made light and compact because the rod exchanging device is supported by the support unit which is provided for the machine body and accordingly a large bending load is not applied to the main body portion of the rod exchanging device.