A lock device is provided with a housing, a rotary member, a pair of link rods provided with a hook part, a spring for the rotary biasing of the rotary member, and an operative member mounted so as to be able to be inserted into the housing. A cam protrusions formed in the rotary member, and a wall part having a cam slope which abuts the cam protrusion is formed in the operative member. The configuration is such that by inserting the operative member, the rotary member resists the biasing force of the spring and rotates, and the hook part of the link rods slides in a position in which it does not engage with the lock part.