A steam sterilizer is provided. A lid opening and closing a vertical chamber opened in the top surface of a body portion is structured so as to be opened and closed up and down by the rotation of a handle shaft vertically helically threaded to an arm with one end thereof supported on the top surface of the body portion in a horizontal movement manner. In a steam sterilizer, a safety device is provided which prevents a lid from opening by unaware operation of a handle when pressure in the chamber is high. The steam sterilizer includes a locking solenoid device which prohibits the rotation of the handle through extension of a locking pin which extends in non-electrified condition and extracts in electrified condition. In the condition that the chamber is closed by the lid, the locking pin is extended as the locking solenoid device is non-electrified, thereby prohibiting the rotation of the handle in the opening direction of the lid.
