To provide a crescent sensor unit usable by being installed in a sash frame, and capable of simultaneously locking a crescent lock together, by detecting an opening-closing state of a sash and a locking-unlocking state of the crescent lock.

This crescent sensor unit is composed of a base part and a body of moving while being supported by the base part. The body is held in a non-hindering range to operation of a lever of the crescent lock before moving from the base part, and is held in a position for physically checking the movement of the lever of the crescent lock stopped in a locking completing position after moving. The body is provided with a reed switch for detecting a sash opening-closing detecting magnet of approaching in a sash closing state, and a lever detecting part for detecting the lever of the crescent lock stopped in the locking completing position.