range of the connector 18 which thus can be turned to a locked or unlocked position the first return spring 17 is then forced from the condition of fig2 to the state of fig2 while the cylindrical portion 19 is moved from the locked position of fig4 to the rotated condition of fig2 when manual operation force is released from the rotated key the second return spring 34 positioned between casing 11 and connector 18 forcibly and elastically pushes the connector 18 sleeve 12 and key cylinder 14 to return from the rotated position of fig1 to the initial position of fig1 in the angular range of rotation of connector 18 subsequently the key cylinder 14 is forced to return from the position of fig1 to the initial position of fig1 by virtue of elastic force of the first return spring 17 within the angular range for sliding of the pin 16 which is then radially and inwardly moved by elastic force of the spring 21 to the initial position on the other hand if the key cylinder 14 is rotated by an incorrect key it is moved from the locked condition of fig2 to the condition of fig1 while the key cylinder 14 is retained in engaged condition with the sleeve.