When a voltage is supplied from a voltage supply terminal to a non-inverted input terminal of an operational amplifier, a voltage equal to the supply voltage is input to an inverted input terminal and also to a voltage apply terminal for a load. When PNP transistors constituting a current mirror turn on in response to the applied voltage, a source current flows through one of the PNP transistors to the load, and a mirror current of the source current flows through the other of the PNP transistors to a current measuring terminal. The current driven to the load can be obtained by measuring the mirror current with an amperemeter.