Abstract: A pivot pin (5) is pivotably provided on a door B through a support member (2). A basal end portion of a pivotal lever (3) is nonpivotably connected to the pivot pin (5). By sandwichingly holding the pivot pin (5) from its both sides by means of a plate spring (4), the pivotal lever (3) is restrained in a lock position and in a release position. The plate spring (4) biases the pivotal lever (3) towards the lock position side through the pivot pin (5), when said pivotal lever (3) is within a range where said pivotal lever (3) is offset a predetermined return angle from the lock position. The pivotal lever (3), which has been forcibly pivoted from the lock position towards the release position side by the forced pivoting portion (11a), is pivoted towards the lock position side by the biasing force of the plate spring (4) and a connecting portion (32) of the pivotal lever (3) is retained between an engagement pin (12) of a retaining member (1) and the forced pivoting portion (11a).