PURPOSE: To easily detect whether sterilization is performed or not by easily detecting the opening of a latch mechanism by a method wherein a cover is locked onto a case with a latch mechanism, an indicating member is inserted into the latch mechanism and the indicating member is provided with a retaining protrusion piece and a swelling stopper section, and further, with a display body discoloring under heating.

CONSTITUTION: An indicating member 151 for locking a cover C onto a case 4 has a pointed head 155 having a body part 153 and a swelling stopper section 157 at an opposite end thereof. the body part 153 is provided with a neck-shaped part 159, and the portion of a long part 160 is provided with a retaining protrusion piece 162. This cone part 162 plays a role of a stopper to prevent a pulling off. The indicating member 151 is provided with a display body discoloring depending on temperature, for example, by using a thermosensitive material at a blade-shaped end to indicate that the case is sterilized by steam or a gas. As a latch plate 106 is turned upward, a part with a sectional area reduced breaks.