Patent Publication Number: US-7586030-B2

Title: Keyboard apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   This invention relates to a keyboard apparatus, and specifically relates to a keyboard apparatus which comprises a key unit provided with a plurality of key bodies, a key supporting part for supporting each key body and a connecting part connecting the key supporting part in a pivotable manner, which are provided integrally by means of synthetic resin, and a key frame on which a key mounting part for locking the key supporting part of the key unit is provided. 
   2. Background Art 
   A keyboard apparatus as shown in  FIG. 17  is disclosed for example in Japanese Patent No. 3082696. As shown in the same drawing, a keyboard apparatus comprises a white key unit  10  and a black key unit  11  serving as key units, and a key frame  20 . The white key unit  10  and the black key unit  11  are, respectively, provided with one or more of key body  12  for stroking operation, a key supporting part  13  supporting the far end of the key body  12  remote from a player in a depth direction Y 1  of the key frame  20 , and a connecting part  14  connecting the key body  12  to the key supporting part  13  in a pivotable manner in a key-stroking direction Y 2 . These parts are provided integrally by means of synthetic resin. 
   The key supporting parts  13  of the white key unit  10  and the black key unit  11 , respectively, have a first screw hole  16  into which a screw N for mounting to the key frame  20  is inserted. The far side remote from a player of the key supporting part  13  of the black key unit  11  is provided with an arm section  13 A extending toward the lower side of the key frame  20  and a first engagement section  13 B provided at the lower end of the arm section  13 A which projects toward the far side from a player. 
   The key frame  20  has an upper surface portion  22  and a first reinforcement rib  23 . The upper surface portion  22  is provided like a plate approximately perpendicular to the key-stroking direction Y 2 . The far side of the upper surface portion  22  away from a player in the depth direction Y 1  is provided with a key mounting part  22 A to which the key supporting part  13  is locked. 
   The key mounting part  22 A has a boss  21  extending toward the lower side, and the boss  21  has a second screw hole  21 A. The second screw hole  21 A has a thread groove to threadably mate with the screw N. The upper surface portion  22  disposed on the farther side than the key mounting part  22 A from a play has an insertion hole  29  into which the first engagement section  13 B is inserted. The first reinforcement rib  23  is provided at the lower side of the upper surface portion  22  of the key frame  20 , and serves to reinforce the key mounting part  22 A which not so strong against applied force. 
   Next, described below is the mounting work of the white key unit  10  and the black key unit  11  having the configurations as described above to the key frame  20 . First, the key supporting parts  13  of two white key units  10  are placed with one laid on another so that their first screw holes  16  in the key mounting parts  13  are aligned. On them, the key supporting part  13  of a black key unit  11  is laid so that their first screw holes  16  are aligned. 
   Then, with the key supporting part  13  of one black key unit  11  are laid on those of two white key units  10 , the first engagement section  13 B of the black key unit  11  is inserted into the insertion hole  29 . This engages the first engagement section  13 B and a second engagement section  27 A which is the edge portion of the far side of the insertion hole  29  away from a player, so that the white key units  10  and the black key unit  11  are temporarily fixed to the key frame  20 . This temporary fixation aligns the first screw holes  16  in the key supporting part  13  of the white key unit  10  and the black key unit  11  with the second screw hole  21 A in the key frame  20 . Then, the screw N is inserted into the first screw holes  16  and threadably mated with the second screw hole  21 A, and the key supporting parts  13  of the white key units  10  and the black key unit  11  are locked to the key mounting part  22 A of the key frame  20 . 
   However, the conventional configuration as shown in  FIG. 17 , which is provided with the first engagement section  13 B projecting below the key mounting part  22 A, has a problem of reducing space efficiency as well as the degree of freedom of mounting component parts such as a hammer, basal plate, cushion and speaker, if mounted below the key mounting part  22 A. 
   In addition, the conventional configuration a shown in  FIG. 17 , which is provided with a boss  21  extending below a key mounting part  22 A of a key frame  20 , has a problem of reducing space efficiency as well as the degree of freedom of mounting due to the boss  21 . It has further problem of interfering with the improvement of production efficiency which can be attained by using standardized screws N, because the screws N need to be longer than ordinary screws in order to be inserted into first screw holes  16  and second screw holes  21 A provided both in the key supporting part  13  and the key frame  20 . 
   The conventional configuration as shown in  FIG. 17 , which is provided with the first reinforcement rib  23  extending below the key mounting part  22 A, has a problem of reducing space efficiency as well as the degree of freedom of mounting also due to the first reinforcement rib  23 . 
   SUMMARY OF THE INVENTION 
   Therefore, it is an object of the present invention, upon focusing on the above-mentioned problems, to provide a keyboard apparatus having improved space efficiency and the degree of freedom of mounting. 
   To solve the above-mentioned problems, there is provided a keyboard apparatus comprising: a key unit that comprises one or more key bodies, a key supporting part for supporting each key body, and a connecting part for connecting the key body to the key supporting part pivotably in a key-stroking direction of the key body; and a key frame that comprises an upper surface, and a key mounting part disposed on the upper surface for locking the key supporting part of the key unit; wherein the key supporting part of the key unit has a first engagement section having a hook-like structure or a press-fitting structure; the key mounting part of the key frame has a second engagement section which engages with the first engagement section when the key unit is mounted to the key frame, the second engagement section having a through-hole or a concave for engagement with the hook-like structure or the press-fitting structure of the first engagement section; and the first engagement section and the second engagement section are located above the key mounting part of the key frame. 
   Preferably, the key supporting part has a first hole; the key mounting part has a projection provided on the upper surface of the key frame and extending toward the key supporting part, and a second hole provided on the projection; and a locking member is inserted into both the first hole and the second hole to lock the key supporting part and the key mounting part with each other. 
   Preferably, the key supporting part has a concave or a mating hole; the key mounting part has a projection provided on the upper surface of the key frame and extending toward the key supporting part; and the projection is inserted into the concave or the mating hole to lock the key supporting part and the key mounting part with each other. 
   Preferably, a plurality of the key units are arranged in a widthwise direction of the key frame; and the key frame has a reinforcement rib which extends toward the key unit and which is positioned in a gap created between the key supporting parts of the key units adjacent to each other in the widthwise direction and also created between the connecting parts belonging to the adjacent key units. 
   Preferably, the key frame is provided with a stopper member disposed adjacent to the second engagement section of the key mounting part of the key frame for restricting a pivotal movement of a hammer member coupled to the key body. 
   There is also provided a keyboard apparatus according to the invention, comprising: a key unit that comprises one or more key bodies, a key supporting part for supporting each key body, and a connecting part for connecting the key body to the key supporting part pivotably in a key-stroking direction of the key body; and a key frame that comprises an upper surface, and a key mounting part disposed on the upper surface for locking the key supporting part of the key unit; wherein the key supporting part of the key unit has a first hole; the key mounting part of the key frame has a projection provided on the upper surface of the key frame and extending toward the key supporting part, and a second hole provided on the projection; and a locking member is inserted into both the first hole and the second hole to lock the key supporting part and the key mounting part with each other. 
   In accordance with embodiments of the invention, since the first engagement section of the key supporting part and the second engagement section of the key mounting part are located above the key mounting part, and accordingly the first engagement section is prevented from being located below the key mounting part, space efficiency as well as the degree of freedom of mounting can be improved. 
   In accordance with the embodiments of the invention, since the projection projecting toward the key supporting part is provided at the key mounting part and the projection has the second hole for inserting a locking member, and accordingly the projection (boss) is prevented from projecting below the key mounting part, space efficiency as well as the degree of freedom of mounting can be further improved. 
   In accordance with the embodiments of the invention, since the projection provided on the upper surface of the key mounting part which projects toward the key supporting part is inserted into the concave or the mating hole on the key supporting part to lock the key supporting part and the key mounting part, and accordingly the projection is prevented from projecting below the key mounting part, space efficiency as well as the degree of freedom of mounting can be further improved. 
   In accordance with the embodiments of the invention, since the reinforcement rib is positioned in the gap between the key supporting part and the connecting part of one key unit and those of another key unit placed next to it, and accordingly the reinforcement rib is prevented from projecting below the key mounting part, space efficiency as well as the degree of freedom of mounting can be further proved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view showing the first embodiment of a keyboard apparatus of the present invention. 
       FIG. 2  is a top view of the keyboard apparatus as shown in  FIG. 1 , with the panel excluded. 
       FIG. 3  is a partial enlarged view in the vicinity of the key supporting part and the key mounting part as shown in  FIG. 1 . 
       FIG. 4  is a top view of a keyboard apparatus according to another embodiment, with the panel excluded. 
       FIG. 5  is a partial cross-sectional view of a keyboard apparatus according to another embodiment. 
       FIG. 6  is a top view of a keyboard apparatus according to another embodiment, with the panel excluded. 
       FIG. 7  is a top view of a keyboard apparatus according to another embodiment, with the panel excluded. 
       FIG. 8  is a cross-sectional view showing the second embodiment of a keyboard apparatus of the present invention. 
       FIG. 9(A)  is a partial top view of the black key unit constituting the keyboard apparatus as shown in  FIG. 8 , and  FIG. 9(B)  is a partial top view of the black key unit and the key frame constituting the keyboard apparatus as shown in  FIG. 8 . 
       FIG. 10  is a partial enlarged view in the vicinity of the key supporting part and the key mounting part of a keyboard apparatus according to another embodiment. 
       FIG. 11  is a partial enlarged view in the vicinity of the key supporting part and the key mounting part of a keyboard apparatus according to another embodiment. 
       FIG. 12  is a partial enlarged view in the vicinity of the key supporting part and the key mounting part of a keyboard apparatus according to another embodiment. 
       FIG. 13  is a cross-sectional view showing the third embodiment of a keyboard apparatus of the present invention. 
       FIG. 14  is a top view of the keyboard apparatus as shown in  FIG. 13 , with the panel excluded. 
       FIG. 15  is a partial enlarged view in the vicinity of the key supporting part and the key mounting part as shown in  FIG. 13 . 
       FIG. 16  is a cross-sectional view showing another embodiment of a keyboard apparatus of the present invention. 
       FIG. 17  is a partial cross-sectional view showing an example of a conventional keyboard apparatus. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   First Embodiment 
   Described below is a first embodiment of the present invention, referring to the drawings.  FIG. 1  is a cross-sectional view showing the first embodiment of a keyboard apparatus  100  of the present invention.  FIG. 2  is a top view of the keyboard apparatus  100  shown in  FIG. 1 , with panel  30  excluded.  FIG. 3  is a partial enlarged view in the vicinity of the key supporting part  13  and key mounting part  22 A of the keyboard apparatus  100  shown in  FIG. 1 . 
   A keyboard apparatus  100 , whose example is an electronic keyboard instrument, comprises a white key unit  10  and a black key unit  11  serving as key units, a key frame  20  formed of hard synthetic resin, and a hammer member  40 , and a panel  30  is provided above as well as in the rear of the keyboard apparatus  100 . 
   The white key unit  10  and black key unit  11  are, respectively, provided with one or more of key body  12  for stroking operation, a key supporting part  13  supporting the farther side of the key body  12  (the rear of the keys) away from a player in a depth direction Y 1 , and a connecting part  14  connecting the key body  12  to the key supporting part  13  in a key-stroking direction Y 2  in a pivotable manner. These parts are provided integrally by means of synthetic resin. 
   The key body  12  is provided with a stopper projection  12 G at the lower surface of the rear end thereof. This stopper projection  12 G is provided for preventing the connecting part  14  having hinge structure from breaking, should the key body  12  be pressed strongly or should a younger child lean on the key body  12 . The key supporting part  13  is provided in a lengthy form with its longitudinal direction extending along a widthwise direction Y 3  of the key frame, as shown in  FIG. 2 , and respective key units  10  and  11  are provided as a common base shared by keys in a common manner. As shown in  FIG. 3 , the key supporting part  13  has a positioning convex portion  13 C on the upper side and a positioning concave portion  13 D on the lower side. The positioning convex portion  13 C and the positioning concave portion  13 D are provided so that the positioning convex portion  13 C provided on the lower side of the key supporting part  13  is fit into the positioning concave portion  13 D provided on the upper side of another key supporting part  13  when a plurality of key supporting parts  13  are stacked with each other in the key-stroking direction Y 2 . The positioning convex portion  13 C and the positioning concave portion  13 D facilitate the positioning between the key supporting parts  13 . As shown in  FIG. 1 , the connecting part  14  is positioned between the key body  12  and the key supporting part  13 , and is designed to be thin and to have elasticity, to constitute a hinge structure. 
   The keyboard apparatus  100  has two white key units  10  and one black key unit  11  per octave. In one of the two white key units  10 , a single key supporting part  13  supports three key bodies  12  covering each note of D, F and A. In the remaining one of the two white key units  10 , a single key supporting part  13  supports four key bodies  12  covering each note of C, E, G and B. In the black key unit  11 , a single key supporting part  13  supports five key bodies  12  covering notes of C#, D#, F#, G# and A#. 
   These two white key units  10  and one black key unit  11  constitute one octave of keys with their key supporting parts  13  stacked on each other in the key-stroking direction Y 2 . A plurality of this one octave keys are arranged in the widthwise direction Y 3  of the key frame. The key bodies  12  for C and B notes have cutouts  12 E and  12 F for creating a gap S extending between the key supporting part  13  and connecting part  14  of one white key unit  10  and those of another white key unit  10  placed next to it in the widthwise direction Y 3 . The gap S extends in the depth direction Y 1  of the key frame toward a player side. The key supporting parts  13 , connecting parts  14  and the cutouts  12 E and  12 F are covered with a panel  30  provided on the upper surface side of the key frame and thus not seen from the front. 
   As shown in  FIG. 3 , the white key units  10 , respectively, have a mating hole  15  into which a boss (projection)  21  on the key frame  20 , which is described later, is fit. On the contrary, the black key unit  11  has a first screw hole  16  into which a screw N serving as a locking member which is smaller than the mating hole  15  is inserted. Any or both of these mating hole  15  and screw hole  16  corresponds (or correspond) to a first hole as set forth in claims. 
   The key supporting part  13  of the black key unit  11  has an arm section  13 A (see  FIG. 9(A) ) provided at the end of the farther side of the key supporting part away from a player in the depth direction Y 1  and extending toward the lower side of the key-stroking direction, and a hook-like first engagement section  13 B is provided at the end of the lower side in the depth direction Y 2  of the arm section  13 A and extending toward the farther side from a player in the depth direction Y 1 . The arm section  13 A and the first engagement section  13 B are provided at the key supporting part  13  which is laid at the top of other key supporting part  13  of a plurality of key units  10  and  11  stacked with each other on the key mounting part  22 A. In this embodiment, the arm section  13 A and the first engagement section  13 B are provided so that the tip of the lower side thereof in the key-stroking direction Y 2  is located above the key mounting part  22 A on the upper surface portion  22  of the key frame with the key supporting part  13  of the black key unit  11  laid on the top of the key supporting parts  13  of the two white key units  10  (see  FIG. 8 ). 
   The key frame  20  is mounted on the lower case not shown. Or the frame  20  itself may constitute a lower case. This key fame  20  has the upper surface portion  22 , a first reinforcement rib  23  integrally formed with the depth direction Y 1  below the upper surface portion  22 , a second reinforcement rib  24  formed above the upper surface portion  22 , a front section  25  and a third reinforcement rib  26 , by means of synthetic resin. The upper surface portion  22  is provided to have a plate-like shape approximately perpendicular to the key-stroking direction Y 2  and located on the farther side away from a player in the depth direction Y 1  and upper side of the key-stroking direction Y 2 . The upper surface portion  22  is provided in a tapered shape where, the closer to the player side in the depth direction Y 1 , the closer to the lower side it becomes. 
   The farther side from a player in the depth direction Y 1  of the upper surface portion  22  has the key mounting part  22 A to which the key supporting part  13  is locked. The key mounting part  22 A has a positioning convex portion  22 B and a boss  21  provided on the positioning concave  22 B, as shown in  FIG. 3 . The positioning convex portion  22 B is provided so that it is fit into the positioning concave portion  13 D when the key supporting part  13  is laid on the key mounting part  22 A. The positioning convex portion  22 B and the positioning concave portion  13 D facilitate the positioning of the key supporting part  13  to the key mounting part  22 A. 
   As shown in  FIG. 3 , the farther side from a player in the depth direction Y 1  than the key mounting part  22 A of the upper surface portion  22  is provided with a vertical wall section  22 D extending in the key-stroking direction Y 2  above the key mounting part  22 A. Above the vertical wall section  22 D, a second engagement section  22 E projecting toward the player side in the depth direction Y 1  is provided. That it, the second engagement section  22 E is located above the key mounting part  22 A. The opposing portion of the upper surface portion  22  facing the second engagement section  22 E has a hole  22 C for the prevention of undercut of the second engagement section  22 E. This hole  22 C serves to prevent interference between the upper surface portion  22  and the first engagement section  13 B when the first engagement section  13 B engages with the second engagement section  22 E. 
   The above-mentioned boss  21  is provided, extending toward the upper side of the key-stroking direction Y 2  of the key mounting part  22 A, that is, toward the key supporting part  13 . The boss  21  has a second screw hole  21 A, which serves as a second hole into which a screw N described later is inserted. The second screw hole  21 A has a thread groove to threadably mate with the screw N. 
   The lower surface of the key mounting part  22 A is provided to have a plate-like shape having a concave groove  221  in the widthwise direction Y 3 . The lower surface of the key mounting part  22 A is provided with a after-touch sensor  60 . The after-touch sensor  60  serves as a sensor detecting a stroking pressure when the key body  12  is further pressed down after a normal key pressing, and is constituted by a resistor board having a resistor pattern with its resistance varying according to the pressure, a conductor board having a conductor pattern to be connected to the resistor pattern and a felt, which are laid on each other in this order. The sensor  60  detects contact pressure by bringing into contact with a key by means of the mass  41  of a hammer member  40  when a key is pressed. 
   As shown in  FIG. 1 , the first reinforcement rib  23  supports the lower side of the key-stroking direction Y 2  of the upper surface portion  22 , and reinforces the upper surface portion  22 . The first reinforcement rib  23  is provided to have a plate-like shape approximately perpendicular to the widthwise direction Y 3  and a plurality of the same ribs are arranged along the widthwise direction Y 3  (between B and C keys as well as E and F keys). 
   The second reinforcement rib  24  serves as a reinforcement rib for reinforcing the upper surface portion  22 . As shown in  FIG. 2 , the second reinforcement rib  24  is provided, extending toward the upper side of the key-stroking direction Y 2  from the upper surface portion  22 , so as to be positioned in a gap S between the key supporting part  13 , connecting part  14  and key body  12  of one white key unit  10  and those of another white key unit  10  placed next to it. The second reinforcement rib  24  is provided to have a plate-like shape approximately perpendicular to the widthwise direction Y 3  and a plurality of them are placed along the widthwise direction Y 3 . 
   The front section  25  is provided on the player side in the depth direction Y 1  and at the lower side of the key-stroking direction Y 2 , and its cross-section has concave and convex surfaces. A third reinforcement rib  26  reinforces the front section  25 . The third reinforcement rib  26  is provided to have a plate-like shape approximately perpendicular to the widthwise direction Y 3 , and a plurality of them are arranged along the widthwise direction Y 3 . 
   As shown in  FIG. 1 , the hammer member  40  is constituted by a mass  41  extending in the depth direction Y 1  and a basal section  42  retaining the end of the mass  41 , and is supported by a fulcrum supporting section  29 A provided above the central convex portion  29  of the key frame  20 . At the tip of the basal section  42 , a connecting strip  42 B splitting into upper and lower direction is formed, and mated with a connecting plate  12 B provided at the lower end of the acting section  12 A projecting toward the lower side from the key body  12 . 
   When a key is pressed, the acting section  12 A pushes down the basal section  42 , and the hammer member  40  rotates counterclockwise in  FIG. 1  around the rotating axis  42 A; while, when a key is released, the acting section  12 A pushes up the basal section  42  and the hammer member  40  rotates clockwise in  FIG. 1  around the axis of rotation  42 A. This contributes to giving a touch feeling like an acoustic piano. The key frame  20  is provided with stoppers SD and SU made of felt respectively at the lower end portion and the upper end portion, and these stoppers SD and SU serve to limit the rotating range of the hammer member  40 . Namely, the key frame  22  is provided with the stopper member SU disposed adjacent to the engagement section  27 A of the key mounting part  22 A of the key frame  22  for restricting a pivotal movement of the hammer member  40  coupled to the key body  12 . 
   A basal plate  50  is arranged between the white key units  10  and black key unit  11  and the hammer member  40 , and a key switch  50 A which is turned on/off when a key body  12  is released is mounted on the key switch  50 A. 
   Next, described below is the mounting of the key units  10  and  11  to the key frame  20  in the keyboard apparatus  100  mentioned above. First, the boss  21  on the key frame  20  is mated with the mating hole  15  in the key supporting part  13  of the white key unit  10  consisting of four key bodies  12  covering each note of C, E, G and B and then that of the white key unit  10  consisting of three key bodies  12  covering each note of D, F and A in this order. 
   At this time, as shown in  FIG. 3 , the positioning concave portion  13 D on the key supporting part  13  of the lower white key unit  10  is mated with the positioning convex portion  22 B on the key mounting part  22 A, and the positioning concave portion  13 D on the key supporting part  13  of the upper white key unit  10  is mated with the positioning convex portion  13 C of the key supporting part  13  of the lower white key unit  10 , so that the white key units  10  are positioned at the key mounting part  22 A. 
   The first engagement section  13 B on the key supporting part  13  of the black key unit  11  is engaged with the second engagement section  22 E on the vertical wall section  22 D, so that the black key unit  11  is temporarily fixed to the key frame  20 . At this time, the first engagement section  13 B is engaged with the second engagement section  22 E so that the positioning concave portion  13 D on the key supporting part  13  of the black key unit  11  is mated with the positioning convex portion  13 C on the key supporting part  13  of the upper white key unit  10 . This temporary fixation aligns the second screw hole  21 A on the boss  21  with the first screw hole  16  on the black key unit  11 . Then the screw N is inserted into both the first screw hole  16  and the second screw hole  21 A to lock the key supporting part  13  to the key mounting part  22 A. 
   In accordance with the above-mentioned keyboard apparatus  100 , since the first engagement section  13 B on the key supporting part  13  and the second engagement section  22 E on the key frame  20  are located above the key mounting part  22 A, the first engagement section  13 B on the key supporting part  13  is prevented from being located below the key mounting part  22 A, and accordingly space efficiency as well as the degree of freedom of mounting can be improved. Specifically, since the first engagement section  13 B is prevented from being located below the key mounting part  22 A, the lower surface of the key mounting part  22 A can be formed flat, which enables an after-touch sensor  60  can be arranged on the lower surface of the key mounting part  22 A, as shown in  FIG. 3 . 
   In addition, since the first engagement section  13 B is prevented from being located below the key mounting part  22 A, when a mass  41  is located at the lower side of the key mounting part  22 A, as shown in  FIG. 1 , the pivoting range of the mass  41  is not restricted by the first engagement section  13 B and, accordingly, can be increased. This means that, the axis  42 A (fulcrum) of the hammer member  40  can be located closer to a player than in the conventional configuration, with respect to a same key stroke as that in the conventional configuration (a prescribed vertical travel range of an acting point). Furthermore, a ratio between the distance from the axis  42 A to the rear end of the hammer member  40  and that from the axis  42 A to the acting point can be increased. This contributes to giving a solid massive feel (resistance feel) even though the mass  41  can be reduced and, accordingly, the weight of the keyboard apparatus  100  with a mass  41  can be reduced. 
   Further in accordance with the keyboard apparatus  100  mentioned above, the black key unit  11  can be temporarily fixed to the key frame  20  by engaging the first engagement section  13 B on the key supporting part  13  with the second engagement section  22 E on the key frame  20  and thus the mounting work can be performed easily. 
   Further in accordance with the keyboard apparatus  100  described above, since the key supporting part  13  has a first screw hole  16 , the key mounting part  22 A has a boss  21  extending toward the key supporting part  13  and a second screw hole  21 A on the boss  21 , and the key supporting part  13  is locked to the key mounting part  22 A by inserting the screw N into both the first screw hole  16  and the second screw hole  21 A, the boss  21  can be prevented from projecting below the key mounting part  22 A and, accordingly, space efficiency and the degree of freedom of mounting can be improved. 
   Further in accordance with the keyboard apparatus  100 , as shown in  FIG. 3 , the key supporting part  13  of the white key unit  10  has a mating hole  15  to mate with the boss  21 , and the key supporting part  13  of the white key unit  10  is pinched and locked between the key mounting part  22 A and the key supporting part  13  of the black key unit  11 . This contributes to easy positioning of the white key unit  10  with respect to the key frame  20  just by mating the mating hole  15  with the boss  21 , which facilitates the mounting work. It would be better that the above-mentioned positioning should be kept within the range of the previous process to align the position of the three key units  10  and  11  with the widthwise direction Y 3  and fix them to the key frame  20 . Because the positioning in the depth direction Y 1  has been completed by means of the positioning convex portion  13 D and the positioning concave portion  13 E. Otherwise, this positioning may be left to the boss  21  and the mating hole  15  in both the depth direction Y 1  and the widthwise direction Y 3 , by easing the mating between the positioning convex portion  13 D and the positioning concave portion  13 E by securing a clearance or other means. Furthermore, since the length of the screw N can be reduced, the screw N can be standardized and, accordingly, production efficiency can be improved. Moreover, if the key frame  20  also serves as a instrument case, the boss  21 , which is a drawback in the appearance, can be hidden behind the key supporting part  13  and thus, a neat appearance can be attained and the degree of freedom of design can be improved. 
   Further in accordance with the keyboard apparatus  100  described above, since the second reinforcement rib  24  is positioned in the gap S between the key supporting part  13  and connecting part  14  of one white key unit  10  and those of another white key unit  10  placed next to it, the second reinforcement rib  24  is prevented from projecting below the key mounting part  22 A. Thus the second reinforcement rib  24  is prevented from projecting below the key mounting part  22 A and thus, the space underneath the key mounting part  22 A can be used effectively, which is exemplified by providing an after-touch sensor  60  or increasing the reciprocating range of the mass  41 . 
   Further in accordance with the keyboard apparatus  100  described above, since cutouts  12 E and  12 F are provided in the section covered with the panel  30  of the key body  12 , the gap S is extended toward the player side in the depth direction Y 1 , and the second reinforcement rib  24  is provided so that it is positioned also in the gap S provided by the cutouts  12 E and  12 F, the second reinforcement rib  24  can be increased in size, so that the reinforcement of the key mounting part  22 A can be further strengthened. 
   In the first embodiment described above, a plurality of key bodies  12  are provided for each key supporting part  13 , however, the present invention needs not be limited to such application. It may be applied in such a way that a single key body  12  is provided for each key supporting part  13 , as shown in  FIG. 4 , for example. In this case, a second reinforcement rib  24  may be positioned in the gap S between the key supporting part  13 , connecting part  14  and key body  12  of one white key unit  10  and those of another white key unit  10  placed next to it in the widthwise direction Y 3 . 
   In the first embodiment described above, there is no second reinforcement rib  24  below the key body  12 , however, the present invention needs not be limited to such application. It may be applied in such a way that a second reinforcement rib  24  may also be provided below the key body  12  to further strengthen the key mounting part  22 A, as shown in  FIG. 5 , for example. 
   In the first embodiment described above, cutouts  12 E and  12 F are provided in the key body  12  and a second reinforcement rib  24  is also positioned in the gap S created by the cutouts  12 E and  12 F, however, the present invention needs not be limited to such application. It may be applied in such a way that, if there is no problem in the strength of the key mounting part  22 A, there may be no cutouts  12 E and  12 F in the key body  12 , and a second reinforcement rib  24  may be positioned only in the gap S between the key supporting part  13  and the connecting part  14 , as shown in  FIGS. 6 and 7 , for example. 
   In the first embodiment described above, a second reinforcement rib  24  is positioned in a gap S between the key supporting part  13 , connecting part  14  and key body  12  of one white key unit  10  and those of another white key unit  10  placed next to it, however, the present invention needs not be limited to such application. It may be applied in such a way that a second reinforcement rib  24  may be provided at the farther side away from a player in the depth direction Y 1  than the key mounting part  22  on the upper surface portion  22 , for example. In this case, however, a stopper SD should be provided below the second reinforcement rib  24 . 
   In the first embodiment described above, the space underneath the key mounting part  22 A is effectively used by providing an after-touch sensor  60  or a mass  41  in the space underneath the key mounting part  22 A, however, the present invention needs not be limited to such application. It may be applied in such a way that the space underneath the key mounting part  22 A is used fro positioning various kinds of functional component such as speaker SP in the space underneath the key mounting part  22 A, for example, as the second embodiment below. 
   Second Embodiment 
   Next described below is the second embodiment of the present invention, referring to the drawings.  FIG. 8  is a cross-sectional view showing the second embodiment of a keyboard apparatus  100  of the present invention.  FIG. 9(A)  is a partial top view showing the black key unit  11  constituting the keyboard apparatus  100  shown in  FIG. 8 .  FIG. 9(B)  is a partial top view of the black key unit  11  and the key frame  20  constituting the keyboard apparatus  100  shown in  FIG. 8 . In  FIGS. 8 and 9 , the parts common to those described in the first embodiment described above referring to  FIGS. 1 through 3  are given the same numerals, respectively, and the detailed description of such parts are omitted. 
   A keyboard apparatus  100  comprises a white key unit  10  and black key unit  11 , and a key frame  20 . The second embodiment differs greatly from the first embodiment in the point that it does not comprise a hammer member  40 . Both the white key unit  10  and black key unit  11  are provided with one or more of key body  12 , a key supporting part  13  and a connecting part  14 , which are provided integrally by means of synthetic resin, similarly to those in the first embodiment. In the second embodiment, the connecting part  14  is constituted by a horizontal wide section  14 A wider than that of the key body  12  and a pair of plate-like thin hinge sections  14 B connecting to both ends of the wide section  14 A, and the other ends of the pair of thin hinge sections  14 B connect to the key supporting part  13 . This contributes to controlling the runout of the key body  12  in the widthwise direction, and thus enables the key body  12  to be vertically reciprocated at a constant position as if so-called key guides are provided, even if there is no key guides. Please note that, for the clarity of the drawing, the structure of the connecting part  14  is shown of only one white key unit  10  in  FIG. 9(A) , however, other white key units  10  and black key units  11  have the same structure as that, respectively. 
   The key body  12  comprises a leg section  12 C extending toward the lower side of the key-stroking direction Y 2 , and a stopper strip  12 D provided at the end of the lower side of the key-stroking direction Y 2  of the leg section  12 C and extending toward the farther side from a player in the depth direction Y 1 . When the key body  12  is pressed down, the lower side of the leg section  12 C is brought into contact with a stopper member SD (made of felt or the like) on the key frame  20 ; while, when the key body  12  is released, the upper side of the stopper strip  12 D is brought into contact with a stopper member SU on the key frame  20  to control the reciprocating range of the key body  12 . The detailed description of the key body  12 , key supporting part  13  and connecting part  14 , which are the same as those in the first embodiment described above, is omitted. 
   The key frame  20  is provided with a top surface portion  22 , a first reinforcement rib  23 , a front section  25 , a third reinforcement rib  26 , a rear wall section  27  and a basal plate mounted section  28 , which are provided integrally by means of synthetic resin. The detailed description of the upper surface portion  22 , front section  25  and third reinforcement rib  26 , which are the same as those in the first embodiment described above, is omitted here. The first reinforcement rib  23  is provided on the lower side of the key-stroking direction Y 2  of the upper surface portion  22  and basal plate mounting section  28  to strengthen them. 
   The rear wall section  27  is provided to have a plate-like shape approximately perpendicular to the depth direction Y 1 , and provided on the farther side away from a player in the depth direction Y 1  of the upper surface portion  22 . The opposing portion  271  facing the first engagement section  13 B of the rear wall section  27  is provided so that its upper end in the key-stroking direction Y 2  is extending above the key mounting part  22 A slightly extending from the upper surface portion  22 , and its upper end is provided with a second engagement section  27 A extending toward a player in the depth direction Y 1  of the key frame. 
   The opposing portion facing the second engagement section  27 A of the upper surface  22  has a hole  22 C for the prevention of undercut of the second engagement section  27 A. This hole  22 C serves to prevent interference between the upper surface portion  22  and the first engagement section  13 B when the first engagement section  13 B engages with the second engagement section  27 A. The arm section  13 A and first engagement section  13 B of the black key unit  11  are provided at two locations corresponding to the C# key and A# key for each key unit of one octave, and the second engagement section  27 A on the key frame  20  side is also located, respectively, at a position corresponding to the first engagement section  13 B. 
   The basal plate mounting section  28  is provided between the upper surface portion  22  and the front section  25 . The basal plate mounted section  28  is located below the upper surface portion  22  and provided with a basal plate  50  having a key switch  50 A on it. 
   Next, the mounting of the key units  10  and  11  to the key frame  20  is described of the keyboard apparatus  100  having the configuration described above. First, a boss  21  on the key frame  20  is mated with the mating holes  15  on the key supporting parts  13  of two white key units  10  in this order. The first engagement section  13 B on the key supporting part  13  of the black key unit  11  is engaged with a second engagement section  27 A on the rear wall section  27  to temporarily lock the black key unit  11  to the key frame  20 . This temporary fixation causes a first screw hole  16  on the key supporting section  13  of the black key unit  11  to be aligned with a second screw hole  21 A on the boss  21 . Then a screw N is inserted into both the first screw hole  16  and the second screw hole  21 A to lock the key units  10  and  11  to the key frame  20 . 
   In accordance with the second embodiment described above, since the first engagement section  13 B on the key supporting part  13  and the second engagement section  27 A on the key frame  20  are located above the key mounting part  22 A, the first engagement section  13 B on the key supporting part  13  is prevented from being located below the key mounting part  22 A. Thus, similarly to that in the first embodiment, the first engagement section  13 B is prevented from projecting below the key mounting part  22 A, various kinds of functional parts such as speaker SP can be positioned below the key mounting part  22 A. 
   As described above, the key supporting part  13  has the first engagement section  13 B. The key mounting part  22 A has the second engagement section  27 A comprised of a projection provided on the upper surface of the key frame and extending toward the key supporting part and a second hole provided on the projection. The locking member N couples the first engagement section  13 B and the second engagement section  27 A with each other to lock the key supporting part  13  and the key mounting part  22 A with each other. 
   In accordance with the second embodiment described above, the black key unit  11  can be temporarily locked to the key frame  20  by engaging the first engagement section  13 B on the key supporting part  13  with the second engagement section  27 A on the key frame  20 , thereby facilitating the mounting work, similarly to that in the first embodiment. 
   In the second embodiment described above, the space underneath the key mounting part  22 A is effectively used by positioning various kinds of functional parts such as speaker SP below the key mounting part  22 A, however, the present invention needs not be limited to such application, for example, similarly to the first embodiment. It may be applied in such a way that the space underneath the key mounting part  22 A may be effectively used by providing an after-touch sensor  60  or a mass  41  in the space underneath the key mounting part  22 A. 
   In the first and second embodiments described above, the key units  10  and  11  are temporarily fixed to the key frame  20  by engaging the first engagement section  13 B with the second engagement sections  22 E and  27 A, and then firmly fixed by means of the screw N, however, the present invention needs not be limited to such application. It may be applied in such a way that the key unites  10  and  11  may be firmly fixed to the key frame by engaging the first engagement section  13 B with the second engagement section  22 E and  27 A, without performing fixation by means of the screw N, as shown in  FIG. 10 . 
   As shown in  FIG. 10 , the key supporting part  13  of the black key unit  11  is provided with an arm section  13 E provided on the player side in the depth direction Y 1  and extending toward the lower side of the key-stroking direction Y 2  and a third engagement section  13 F provided at the lower end in the key-stroking direction of the arm section  13 E and extending toward the player side in the depth direction Y 1 . The upper surface portion  22  of the key frame  20  has an insertion hole  22 F into which the third engagement section  13 F is inserted. Inserting the third engagement section  13 F into the insertion hole  22 F engages the third engagement section  13 F with a fourth engagement section  22 G located at the edge of the player side of the insertion hole  22 F. This causes the player side as well as the farther side from the player in the depth direction Y 1  of the key supporting part  13  to be engaged with the key frame  20 , thereby making firm fixation only by means of the engagement sections  13 A and  13 F without using the screw N. 
   As shown in  FIG. 11 , the key units  10  and  11  may be firmly fixed to the key frame  20  by engaging the first engagement section  13 B with the second engagement sections  22 E and  27 A without performing fixation by the screw N. 
   As shown in  FIG. 11 , the key mounting part  22 A has a boss  21  extending toward the key supporting section  13 . The lower side of the key supporting part  13  of the black key unit  11  has a concave portion  13 G having a concavity on the upper side. Mating the boss  21  with the concave portion  13 G to lock the key supporting part  13  and the key mounting part  22 A can firmly fix them just by means of the first engagement section  13 B and the concave portion  13 G without using a screw N. 
   In such a case as shown in  FIG. 11 , the boss  21  can be prevented from projecting below the key mounting part  22 A, thereby improving space efficiency and the degree of freedom of mounting. 
   In the example as shown in  FIG. 11 , the key supporting part  13  has a concave portion  13 G, into which the boss  21  is mated with, however, the present invention needs not be limited to such application. It may be applied in such a way that the key supporting part  13  of the black key unit  11  may be provided with a mating through-hole in the key-stroking direction Y 2  and the boss  21  may be mated with the mating hole. 
   In the first and second embodiments, the second engagement sections  27 A and  22 E are formed by contact strips extending from the vertical wall section  22 D and the rear wall section  27 , and the contact strips are brought into contact with each other, however, the present invention needs not be limited to such application. It may be applied in such a way that, as shown in  FIG. 12 , the second engagement section  27 A may be formed as an engagement section having a through-hole  27 A 1 , and the first engagement section  13 B formed in press-fitting structure may be press-fitted into the through-hole  27 A 1 . The press-fitting structure of the first engagement section  13 A enables the first engagement section  13 A to be press-fitted into the through-hole  27 A 1  provided on the second engagement section  27 A, which is provided in a rod-like shape in the embodiment as shown in  FIG. 12 , with its end portion tapered toward the tip. In the embodiment as shown in  FIG. 12 , the second engagement section  27 A has a through-hole  27 A 1 , however, a concave portion may be provided instead of the through-hole  27 A 1 , so that the first engagement section  13 A may be press-fitted into the concave portion. 
   In the first and second embodiments described above, the key supporting part  13  of the white key unit  10  has a mating hole  15  and the boss  21  is mated with the mating hole  15 , however, the present invention needs not be limited to such application. It may be applied in such a way that, as shown in  FIG. 12 , the key supporting part  13  may respectively have a screw insertion hole (unloaded hole)  16 ′, the two white key units  10  and the black key unit  20  may be laid on the boss  21  in the order as shown in the figure, with the screw N inserted into the screw insertion holes  16 ′, so that they can be threadably mated with the screw  21 A and locked to the key mounting part  22 A. In this case, the positioning of the key units  10  and  11  to the key frame  20  is made with the through-hole  27 A 1  and the projection of the first engagement section  13 B. 
   In the first and second embodiments, the screw N is used as a locking member, however, the present invention needs not be limited to such application. It may be applied in such a way that the locking member may be press-fitted into both the first hole (first screw hole) on the key supporting part  13  and the second hole (second screw hole) on the key mounting part  22 A to lock the key supporting part  13  to the key mounting part  22 A. Generally, the locking member comprises a screw, a hook or both of the screw and hook. 
   The embodiments described above suggest only the typical modes of the present invention and the application of the present invention may not be limited to the suggested embodiments. Therefore, one ordinarily skilled in the art can made various changes and modifications to the present invention without departing from the spirit and scope of the present invention. 
   Third Embodiment 
   Described below is a third embodiment of the present invention, referring to the drawings.  FIG. 13  is a cross-sectional view showing the third embodiment of a keyboard apparatus  100  of the present invention.  FIG. 14  is a top view of the keyboard apparatus  100  shown in  FIG. 13 , with panel  30  excluded.  FIG. 15  is a partial enlarged view in the vicinity of the key supporting part  13  and key mounting part  22 A of the keyboard apparatus  100  shown in  FIG. 13 . 
   A keyboard apparatus  100 , whose example is an electronic keyboard instrument, comprises a white key unit  10  and a black key unit  11  serving as key units, a key frame  20  formed of hard synthetic resin, and a hammer member  40 , and a panel  30  is provided above the key frame as well as in the rear of the keyboard apparatus  100 . 
   The white key unit  10  and black key unit  11  are, respectively, provided with one or more of key body  12  for undergoing stroking operation, a key supporting part  13  supporting the farther side of the key body away from a player in a depth direction Y 1  of the key body  12 , and a connecting part  14  connecting the key body  12  to the key supporting part  13  pivotably in a key-stroking direction Y 2 . These parts are provided integrally by means of synthetic resin. 
   The key body  12  is provided with a stopper projection  12 G at the lower surface of the rear end of the key body. This stopper projection  12 G is provided for preventing the connecting part  14  having hinge structure from breaking, should the key body  12  be pressed strongly or should a younger child lean on the key body  12 . The key supporting part  13  is provided in a lengthy form with its longitudinal direction extending along a widthwise direction Y 3 , as shown in  FIG. 14 , and respective key units  10  and  11  are provided as a common base shared by keys in a common manner. As shown in  FIG. 15 , the key supporting part  13  has a positioning convex portion  13 C on the upper side and a positioning concave portion  13 D on the lower side. The positioning convex portion  13 C and the positioning concave portion  13 D are provided so that the positioning convex portion  13 C provided on the lower side of the key supporting part  13  is fit into the positioning concave portion  13 D provided on the upper side of another key supporting part  13  when a plurality of key supporting parts  13  are superposed each other in the key-stroking direction Y 2 . The positioning convex portion  13 C and the positioning concave portion  13 D facilitate the positioning between the key supporting parts  13 . As shown in  FIG. 13 , the connecting part  14  is positioned between the key body  12  and the key supporting part  13 , and is designed to be thin and to have elasticity, to constitute a hinge structure. 
   The keyboard apparatus  100  has two white key units  10  and one black key unit  11  per octave. In one of the two white key units  10 , a single key supporting part  13  supports three key bodies  12  covering each note of D, F and A. In the remaining one of the two white key units  10 , a single key supporting part  13  supports four key bodies  12  covering each note of C, E, G and B. In the black key unit  11 , a single key supporting part  13  supports five key bodies  12  covering notes of C#, D#, F#, G# and A#. 
   These two white key units  10  and one black key unit  11  constitute one octave of keys with their key supporting parts  13  stacked on each other in the key-stroking direction Y 2 . A plurality of this one octave keys are arranged in the widthwise direction Y 3  of the key frame. The key bodies  12  for C and B notes have cutouts  12 E and  12 F for creating a gap S between the key supporting part  13  and connecting part  14  of one white key unit  10  and those of another white key unit  10  placed next to it in the widthwise direction Y 3 . The gap S extends in the depth direction Y 1  toward a player side. The key supporting parts  13 , connecting parts  14  and the cutouts  12 E and  12 F are covered with a panel  30  provided on the upper surface side and thus not seen from the front. 
   As shown in  FIG. 15 , the white key units  10 , respectively, have a mating hole  15  into which a boss  21  on the key frame  20 , which is described later, is fit. On the contrary, the black key unit  11  has a first screw hole  16  into which a screw N serving as a locking member which is smaller than the mating hole  15  is inserted. Any or both of these mating hole  15  and screw hole  16  corresponds (or correspond) to a first hole as set forth in the claims. 
   The key frame  20  is mounted on the lower case not shown. Or the frame  20  itself may constitute a lower case. This key fame  20  has a upper surface portion  22 , a first reinforcement rib  23  integrally formed along the depth direction Y 1  below the upper surface portion  22 , a second reinforcement rib  24  formed above the upper surface portion  22 , a front section  25  and a third reinforcement rib  26 , by means of synthetic resin. The upper surface portion  22  is provided to have a plate-like shape approximately perpendicular to the key-stroking direction Y 2  and located on the farther side remote from a player in the depth direction Y 1  and upper side of the key-stroking direction Y 2 . The upper surface portion  22  is provided in a tapered shape where, the closer to the player side in the depth direction Y 1 , the closer to the lower side it becomes. 
   The farther side remote from a player in the depth direction Y 1  of the upper surface portion  22  has a key mounting part  22 A to which the key supporting part  13  is locked. The key mounting part  22 A has a positioning convex portion  22 B and a boss  21  provided on the positioning concave portion  22 B, as shown in  FIG. 15 . The positioning convex portion  22 B is provided so that it is fit into the positioning concave portion  13 D when the key supporting part  13  is laid on the key mounting part  22 A. The positioning convex portion  22 B and the positioning concave portion  13 D facilitate the positioning of the key supporting part  13  to the key mounting part  22 A. 
   The above-mentioned boss  21  is provided, extending toward the upper side of the key-stroking direction Y 2  of the key mounting part  22 A, that is, toward the key supporting part  13 . The boss  21  has a second screw hole  21 A, which serves as a second hole into which a screw N described later is inserted. The second screw hole  21 A has a thread groove to threadably mate with the screw N. 
   The lower surface of the key mounting part  22 A is provided to have a plate-like shape having a concave groove  221  in the widthwise direction Y 3 . The lower surface of the key mounting part  22 A is provided with a after-touch sensor  60 . The after-touch sensor  60  serves as a sensor detecting a striking pressure when the key body  12  is further pressed down after a normal key pressing, and is constituted by a resistor board having a resistor pattern with its resistance varying according to the pressure, a conductor board having a conductor pattern to be connected to the resistor pattern and a felt, which are laid on each other in this order. The sensor  60  detects contact pressure by bringing into contact with the key body by means of the mass  41  of a hammer member  40  when a key is pressed. 
   The first reinforcement rib  23  supports the lower side of the key-stroking direction Y 2  of the upper surface portion  22  and reinforces the upper surface portion  22 . The first reinforcement rib  23  is provided to have a plate-like shape approximately perpendicular to the widthwise direction Y 3  and a plurality of the same ribs are arranged along the widthwise direction Y 3  (for example, between B and C keys). 
   The second reinforcement rib  24  serves as a reinforcement rib for reinforcing the upper surface portion  22 . As shown in  FIG. 14 , the second reinforcement rib  24  is provided, extending toward the upper side of the key-stroking direction Y 2  from the upper surface portion  22 , so as to be positioned in a gap S between the key supporting part  13 , connecting part  14  and key body  12  of one white key unit  10  and those of another white key unit  10  placed next to it. The second reinforcement rib  24  is provided to have a plate-like shape approximately perpendicular to the widthwise direction Y 3  and a plurality of them are placed along the widthwise direction Y 3 . 
   The front section  25  is provided on the player side in the depth direction Y 1  and at the lower side of the key-stroking direction Y 2 , and its cross-section has concave and convex surfaces. A third reinforcement rib  26  reinforces the front section  25 . The third reinforcement rib  26  is provided to have a plate-like shape approximately perpendicular to the widthwise direction Y 3 , and a plurality of them are arranged along the widthwise direction Y 3 . 
   As shown in  FIG. 13 , the hammer member  40  is constituted by a mass  41  extending in the depth direction Y 1  and a basal section  42  retaining the end of the mass  41 , and is supported by a fulcrum supporting section  29 A provided above the central convex portion  29  of the key frame  20 . At the tip of the basal section  42 , a connecting strip  42 B splitting into upper and lower direction is formed, and mated with a connecting plate  12 B provided at the lower end of the acting section  12 A projecting toward the lower side from the key body  12 . 
   When a key body is pressed, the acting section  12 A pushes down the basal section  42  and the hammer member  40  rotates counterclockwise in  FIG. 13  around the rotating axis  42 A; while, when a key body is released, the acting section  12 A pushes up the basal section  42  and the hammer member  40  rotates clockwise in  FIG. 13  around the axis of rotation  42 A. This contributes to giving a touch feeling like an acoustic piano. The key frame  20  is provided with stoppers SD and SU made of felt at the lower end portion and the upper end portion of the key frame, and these stoppers SD and SU serve to limit the rotating range of the hammer member  40 . 
   A basal plate  50  is arranged between the white key units  10  and black key unit  11  and the hammer member  40 , and a key switch  50 A which is turned on/off when a key body  12  is released is mounted on the key switch  50 A. 
   Next, described below is the mounting of the key units  10  and  11  to the key frame  20  in the keyboard apparatus  100  mentioned above. First, the boss  21  on the key frame  20  is mated with the mating hole  15  in the key supporting part  13  of the white key unit  10  consisting of four key bodies  12  covering each note of C, E, G and B and then that of the white key unit  10  consisting of three key bodies  12  covering each note of D, F and A in this order. 
   At this time, as shown in  FIG. 15 , the positioning concave portion  13 D on the key supporting part  13  of the lower white key unit  10  is mated with the positioning convex portion  22 B on the key mounting part  22 A, and the positioning concave portion  13 D on the key supporting part  13  of the upper white key unit  10  is mated with the positioning convex portion  13 C of the key supporting part  13  of the lower white key unit  10 , so that the white key units  10  are positioned at the key mounting part  22 A. 
   The key supporting part  13  of the black key unit  11  is laid on the key supporting part  13  of the white key unit  10  so that the positioning convex portion  13 C provided on the key supporting part  13  of the upper white key unit  10  is fit into the positioning concave portion  13 D provided on the key supporting part  13  of the black key unit  11 . This aligns the second screw hole  21 A provided on the boss  21  with the first screw hole  16  provided on the black key unit  11 . Then the screw N is inserted into both the first screw hole  16  and the second screw hole  21 A to lock the key supporting part  13  and the key mounting part  22 A with each other. 
   In accordance with the keyboard apparatus  100  described above, since the key supporting part  13  has the first screw hole  16 , the key mounting part  22 A has a boss  21  extending toward the key supporting part  13  and a second screw hole  21 A provided on the boss  21 , and the screw N is inserted into both the first screw hole  16  and the second screw hole  21 A to lock the key supporting part  13  and the key mounting part  22 A, the boss  21  is prevented from projecting below the key mounting part  22 A, and space efficiency as well as the degree of freedom of mounting can be improved. Specifically, since the boss  21  is prevented from projecting below the key mounting part  22 A, an after-touch sensor  60 , for example, can be arranged on the lower surface of the key mounting part  22 A, as shown in  FIG. 13 . 
   In addition, when a mass  41  is located at the lower side of the key mounting part  22 A, as shown in  FIG. 13 , the reciprocating range of the mass  41  is not restricted by the key mounting part  22 A, accordingly, can be increased. This means that, the axis  42 A (fulcrum) of the hammer member  40  can be located closer a player than in the conventional configuration, with respect to a same key stroke as that in the conventional configuration (a prescribed vertical travel range of an acting point). Furthermore, a ratio between the distance from the axis  42 A to the rear end of the hammer member  40  and that from the axis  42 A to the acting point can be increased. This contributes to giving a solid massive feel (resistance feel) even though the mass  41  can be reduced and, accordingly, the weight of the keyboard apparatus  100  with a mass  41  can be reduced. 
   In the third embodiment described above, the second reinforcement rib  24  is positioned in a gap S created between the key supporting part  13 , connecting part  14  and key body  12  of the white key unit  10  and those of the white key unit placed next to it in the widthwise direction Y 3 , however, the present invention needs not be limited to such application. For example, as shown in  FIG. 16 , it may be applied in such a way that a second reinforcement rib  24  may be provided on the farther side from a player in the depth direction Y 1  than the key mounting part  22 A of the upper surface portion  22 . In this case, however, a stopper SU should be provided below the second reinforcement rib  24 .