with the stereo headphone 8 being connected thereto therefore stereo sounds can be enjoyed while the main module 1 is carried as a portable unit in this case the main module 1 of the tape recorder is used as a means for reproducing or playback only when the main module 1 is coupled with the adapter module 9 as shown in fig2 the reproducing circuit and the recording circuit which are both not shown are automatically connected to the main module 1 through the connector at the same time the small diameter portion 241 of the flywheel 24 in the tape driving mechanism 18 of the adapter module 9 is inserted into the main module 1 so that the friction member 25 in the free end portion of the small diameter portion 241 is pressingly contacted against the peripheral surface of the pulley 31 in the tape drive system 19 of the main module 1 through the bias force by the spring 28 in this state the tape recording device composed of the main module 1 and the adapter module 9 is set on the recording mode or the reproducing mode therefore the flywheel 24 is rotated by the motor 20 when it is started through the belt 26 so that through the friction member 25 of the small diameter portion 241 the pulley 31 of the tape drive system 19 of the main module 1 is rotated thereby to rotate the capstan 29 meanwhile in the main.