To provide a both-sided locking device for a door, reducing the material cost and assembling cost of a part, and precisely preventing damage due to thumb turn.

In this both-sided locking device for a door, the exterior side of a door is provided with a cylinder lock mechanism, the interior side of the door is provided with a thumb turn mechanism, and an interlocking mechanism is provided to convert each rotary movement of a locking shaft of the cylinder lock and an operating shaft of the thumb turn mechanism to the projecting and sinking movement of a dead bolt. A key receiving hole is provided in the inner end face of the operating shaft of the thumb turn mechanism, and a key of the cylinder lock mechanism is used as an operating knob of the thumb turn mechanism.