According to a certain embodiment, a pin plunger includes: a first contact member; a second contact member that faces the first contact member and is apart from the first contact member; a spring arranged between the first contact member and the second contact member; and a housing that houses the first contact member, the second contact member, and the spring. The housing comprises a bimetal inside or outside the housing. The bimetal comprises a first metal and a second metal, the first metal having a thermal expansion coefficient different from a thermal expansion coefficient of the second metal. The elastic force decreased or increased by contracting or expanding of the spring due to a temperature change is compensated with a warping force due to stretching of the first metal and the second metal.