A tank body 3 is formed in the shape of an elongated groove having an intermediate first slit 5 disposed at its middle portion in the longitudinal direction and having a pair of end first slits 5a disposed at its opposite ends. The assembly rotatably mounts an access door for a compartment of the refrigerator to part of refrigerator that defines the compartment. The first ferromagnetic layer includes: a first portion having an end face located in the detection surface and a rear end opposite to the end face; and a second portion located away from the detection surface and connected to the rear end of the first portion.