one in step s45 a decision is made as to whether the control button 21 was operated again if not the operation returns to step s43 until the control button 21 is operated and each time the right number r is increased by one when the control button 21 is operated the operation proceeds to step s46 and the two digit inputted number lr is stored as the password pw in the memory component 30 a password pw is thus registered after being selected from among 100 two digit numbers lr ranging from 34 00 34 to 34 99 34 returning to fig1 the operation proceeds to step s32 if it is decided in step s23 that the control button 21 was operated during unlocking in step s32 the left number l is increased by one just as when the password was registered if it is decided that the control button 22 was operated the operation proceeds from step s24 to step s33 in step s33 the right number r is increased by one just as when the password was registered if the entered number lr matches the password pw in step s25 the operation proceeds to step s34 and the actuation position vp is set to first gear v1 in other words the sleeve 77 is rotated by the shift motor 29 and positioned at the first gear v1 thus releasing the engagement between the lock ring 114 and the serration teeth 113 of the hub shell 43 thereafter when the bicycle is pedaled the rotation of the driver 42 is transmitted unchanged to the.