8 is long enough to slack when the top board 2 is closed as shown in fig1 in order to incorporate the keyboard into the musical instrument the keys 7 are assembled to the frame 5 and the frame 5 is in turn coupled to the key blocks 1 then the front cover 9 is turned upwards about its rear hinges 92 when the front cover 9 is turned to a certain extent the rear end of the stay 91 of the front cover 9 abuts on the first pins 31 on the side boards 3 see fig4 that is in the case of this embodiment the first pins 31 act as a kind of stopper for the front cover 9 next the keyboard with the key blocks 1 and the frame 5 is inserted from the front side until the first transverse grooves 11 in the key blocks 1 fully engage with the first pins 31 on the side boards 3 thereafter the keyboard is turned downwards about the first pins 31 until the second transverse grooves 12 in the key blocks 1 fully engage with the second pins 32 on the side boards 3 finally the frame 5 is fixed to the bottom board 4 via set bolts 41 in order to have an access to the bottom construction of the keyboard it is necessary to turn the keyboard upwards about the first pins 31 on the side boards 3 consequently the control panel 6 must be placed out of the moving ambit of the keyboard when the latter.