To provide a discharge circuit largely reduced in power loss during an operation in comparison with a conventional discharge circuit, and preventing the complicatedness of a control.

The constant-power discharge circuit 1 is composed of: a transistor Q adjusting a discharge current ID by a gate voltage; a shunt resistor RD' outputting a reference voltage ER proportional to the discharge current ID adjusted by the transistor Q; and a constant-power control circuit 3 determining a discharge-current set value ID* in response to a residual voltage EC gradually lowered by a discharge while controlling the gate voltage so that the discharge current ID is equalized to the discharge-current set value ID* by comparing the set value ID* and the reference voltage ER. The constant-power control circuit 3 compares the residual voltage EC and a comparison voltage preset in response to one or more changed nodes, and changes the discharge-current set value ID* when the residual voltage EC is lower than the comparison voltage.