A fixing device includes a first fixing member, a second fixing member, a heater, a temperature sensor, a sensor holder, and a first frame. The temperature sensor detects a temperature of the first fixing member or the second fixing member. The sensor holder is configured to hold the temperature sensor and is fixed on the first frame. The first frame is made of metal and includes a first bend, a second bend, a third bend, a first wall, a second wall, a third wall, and a fourth wall. The second wall is connected to the first wall via the first bend. The third wall is connected to the second wall via the second bend. The fourth wall is connected to the third wall via the third bend. The first wall and the second wall form an acute angle.