To provide a lock device for a bicycle capable of properly maintaining a locking/releasing condition, and capable of releasing it by remote control.

In a lock device for a bicycle consisting of a first constituent element having a transmitting means for an identification signal, a second constituent element having a control means for identifying and judging a received signal and for transmitting an operation signal on the basis of the judment, and a third constituent element provided with both a lock body for slidably holding a latch formed into a curved shape and energized so as to be drawn in a releasing position by a spring and an electric actuator for releasing the lock of a lock mechanism on the basis of the signal sent from a control means, engaging cutout parts 38, 39 to respective lock mechanism are provided in the parts corresponding to both the locking position of the latch 33 and the releasing position thereof.