Provided is a relay unit that is inexpensive and has a long life, and a method for controlling a relay circuit. A series circuit of mechanical switches is connected in series to a load and a load power supply, and a control unit selects one of the mechanical switches as a selected switch, and performs a switching timing shift, which is constituted by at least one of a first operation in which the selected switch is switched to the closed state after the mechanical switch other than the selected switch, and a second operation in which the selected switch is switched to the open state prior to the mechanical switch other than the selected switch.