PURPOSE: To prevent a casing body from being removed from a casing cover, eliminate sealing failure between the casing body and the casing cover and sealing failure which is caused by pulling-out of a connection wire from the casing cover, and reduce weight.

CONSTITUTION: For a casing body 13A housing a leaked liquid detection circuit for detecting whether leaked liquid is absorbed or not by an absorption paper which is laid out at a region for detecting leaked liquid, a casing cover 13B is laid out so that it cannot be removed, the casing body 13A and the casing cover 13B are sealed by an O-ring 13C, and then a connection lead-out part 13B3 of the casing cover 13B is clamped and sealed by a clamping member 13D.