To provide a key hole inside object sensor for making a sensing part hard to be broken down and allowing even a finger-disabled person to easily unlocking.

A lock body 1 is composed of an outer cylinder 2 and a cylinder frame 3 rotatably fitted in the outer cylinder 2. A key hole 4 for inserting a key is formed inside the cylinder frame 3. The sensing part 10 is slidingly inserted into the key hole 4 from an opposite end part 4b of a key inserting port 4a. A stopper 11 is arranged in an opposite end part 10b of a key inserting port side end part 10a of the sensing part 10. A spring 12 having the fixed base end abuts to the opposite end part 10b, and always presses the sensing part 10 in the direction of the key inserting port 4a. A tip part 13a of a sensor 13 installed in the outer cylinder 2 is arranged in the vicinity of the opposite end part 10b of the sensing part 10.