To provide a dimmer for illumination, in which resolution during dimming under low illuminance is improved by a simple circuit system for phase control, while the lowest dimming voltage can be reduced to almost a half of that in the conventional systems, and which can be structured inexpensively.

A circuit is structured, such that it can be interchanged into either a full-wave rectifying circuit or a half-wave rectifying circuit, in which an AC power source 1, diodes 21 to 24 are connected in a bridge connection. That is, this device has a rectifying circuit 2 for rectifying an input voltage from the AC power source 1, a change-over switch 7 for interchanging a circuit structure of the rectifying circuit 2 either for a full-wave rectification or a half-wave rectification, a power control circuit using a thyristor 4 for supplying electric power to a lamp 6 to be dimmed by phase controlling a rectified output of the rectifying circuit. 2 and a dimming part 3. The brightness of the lamp to be dimmed is varied by the dimming part 3 controlling on/off timing of the thyristor 7 of the power control circuit.