A pressure lever journaling a pressure roller is rockably connected to a fixation frame journaling a fixing roller. A pivotal position of the pressure lever is adjusted by a motor through driving gears, sector gears, press-contact adjusting levers, and press contact springs, so that a mode of a fixing press contact force is set to a heavy press contact mode or a light press contact mode. By a control section, at start-up immediately after power-on and on basis of a temperature and a humidity detected by a temperature and humidity sensor, the heavy press contact mode is established for rectifying poor curl conditions of paper sheets on condition that the present temperature and humidity environment is a high-temperature high-humidity environment or the light press contact mode is established for rectifying poor fixation performance on condition that the present temperature and humidity environment is a low-temperature low-humidity environment.