A disclosed fusing device includes a fusing part; a pressing part rotatably pressed against the fusing part to form a fusing nip for fusing a toner image onto a sheet; a capacitor; a center heater for heating a center portion of the fusing part; an edge heater for heating edge portions of the fusing part; an auxiliary heater for heating the fusing part; and a control unit configured to continuously turn off the edge heater and to turn on the center heater and the auxiliary heater to heat the fusing part during a fusing process of one or more small-size sheets having a width less than that of the heat generating portion of the center heater. The control unit is configured to turn on the edge heater to heat the fusing part when the capacitor stops discharging electricity during a consecutive fusing process of multiple small-size sheets.