Fixing device, image forming apparatus and heater power control method

A fixing device comprising:

• a fixing belt which is in a cylindrical shape and heats toner on a medium while rotating around an axis;
• a pressure member which forms a pressure region between the fixing belt and the pressure member, and pressurizes the toner on the medium passing through the pressure region while rotating around an axis;
• a heater which comes into contact with an inner surface of the fixing belt facing the pressure region, receives electric power, generates heat, and heats the fixing belt;
• a belt temperature detection part which detects a temperature of the fixing belt;
• a heater temperature detection part which detects a temperature of the heater;
• and
• a power control part which controls power supplied to the heater, wherein
• the power control part executes a first power supply control for supply power to the heater, in a first control cycle until the heater temperature detection part detects a target temperature and the belt temperature detection part detects a temperature outside a target range,
• when the belt temperature detection part detects a temperature outside the target range, the power control part executes a correction control for correcting the target temperature so that the belt temperature detection part detects a temperature within the target range, and a second power supply control for supplying power to the heater so that the heater temperature detection part detects a corrected target temperature, in a second control cycle set at a time interval 10 times or more the first control cycle.