by controlling the amount of the coil current allows the amount of the electric power supplied to the heating apparatus to fluctuate as the voltage fluctuates thus employment of this method for ordinary appliances which is unrealistic because ordinary appliances are limited in the available amount of electric power when the amount of power p inputted to the magnetic flux generating means is p in the total amount of electrical resistance is r and the current which flows through the coil is i the amount of the current which flows through the circuit can be expressed by the following equation 4 here the ratio between the resistance r nb of the circuit when the magnetism is not blocked and the resistance r b of the circuit when the magnetism is partially blocked can be obtained from the following equation 5 r nb r b r coil r heatr u2014 center r heatr u2014 end r coil r heatr u2014 center r shut 1 56 according to equation 4 if the amount of electric power input p in is controlled so that it remains constant the amount of the current i changes in response to the changes in the value of the resistance r from equation 5 the amount of the current i which flows while the magnetism is not blocked is 1 25 times 1 56 1 2 that which flows while the magnetism is partially blocked in other words the amount of the current i in equation 1 increases therefore if the fixation roller is heated by generating heat therein by supplying the magnetic flux generating means with the same amount.