A position detection device, for detecting a change in relative position of a detection object with respect to a reference portion, includes: a base portion immovable with respect to the reference portion; a following portion deformable or movable following relative movement of the detection object with respect to the reference portion; an expandable and contractible member; and a heat flux detection section. The expandable and contractible member is provided between the base portion and the following portion, is made of a material expandable and contractible according to deformation or movement of the following portion, and generates heat during contraction and absorbs heat during expansion. The heat flux detection section is provided to be subjected to heat of the expandable and contractible member, and is configured to detect a heat flux that is a flow of heat between an inside and an outside of the expandable and contractible member.