To improve the versatility of a push-button locking device by forming a casing as slim as possible so that the push-button locking device can be assembled to a compact part such as a longitudinal frame of a sliding door.

In this push-button locking device 1, a plurality of push-buttons 3 are provided on a face side of a casing 2 in a retractable manner, a locking member movable in the longitudinal direction of the casing 2 is provided in the casing 2, an operation member 6 to move the locking member in the unlocking direction is provided on the casing 2, and the movement of the locking member in the unlocking direction is allowed when a preset unlocking push- button 3A out of a plurality of push-buttons 3 is pushed. In the push-button locking device 1, all push-buttons 3 are arranged in a row on the line in the longitudinal direction, and the operation member 6 is movably provided in the inside to outside direction of the casing 2.