To provide a window locking device capable of locking and unlocking a window by driving force of a motor, and easily and surely locking and unlocking the window manually.

In this window locking device, a crescent 8 is operatively connected to a rotating shaft of the motor rotated in the normal and reverse directions. The device is provided with a driving plate 31 freely rotated according to the rotary drive of the motor 22 and a driven plate 26 integrally rotated with the crescent 8. The operating plate 31 is provided with a pressing part 31a as a driving side abutting part, and the driven plate 26 is provided with a rotating direction front edge 28a and a rotating direction rear edge 28b separated from each other at a designated angle as a driven side abutting part. When one of both abutting parts is rotated at a designated angle either in the normal direction or in the reverse direction, they are abutted and engaged. The rotating shaft of the motor 22 and the crescent 8 are operatively connected through the abutting engagement relationship of both abutting parts.