To provide a platen heater compatible with both domestic AC 100 V power supply and AC 200 V power supply of foreign countries.

When an image is formed, a platen is heated by means of heaters H1, H2 in order to warm a sheet on the platen. A controller detects the power supply voltage when a printer is turned on. The heaters H1, H2 are connected automatically in parallel in case of AC 100 V and connected automatically in series in case of AC 200 V thus keeping the current flowing through the heaters H1, H2 at a constant level.