To provide an inside lock device which facilitates retrofitting thereof.

According to the structure of the inside lock device, when an inside door lever 2 of a door body 1 is constrained in a locking state, an outside door handle 3 operable in interlock with the door lever 2 is inhibited from performing door opening operation. In general, the inside and outside door handles are arranged so as to interlock with each other, and therefore by constraining the inside door handle, the outside door handle is also constrained. Thus by inhibiting the door opening operation on the outside of the door, a latch bolt as a so-called latch can function as a lock, and a locking state of the door body is ensured.