The heat dissipation of a circuit assembly is improved. A circuit assembly includes: a relay that includes a terminal and generates heat when energized/as a result of energization/due to being energized; a base member to which the relay is attached and in which a through hole is formed; a heat dissipation member that is provided on a side of the base member opposite to a side on which the relay is attached; a first busbar that is connected to the terminal of the relay at a position spaced apart from the base member; and a heat transfer member that is inserted into the through hole so as to be movable in a direction along the axial direction of the through hole, and that comes into contact with the first busbar and the heat dissipation member.