Heat device and image forming apparatus including the same

Provided is a heat device which heats and fixes a developed image onto a recording material while nipping and conveying the recording material bearing the developed image by a nip portion, in which even when a turn-on duty ratio between at least two heat generation members provided to a heat source is switched in a direction in which a maximum amount of possible heat generation is decreased, in order to suppress generation of a fixing failure of the developed image formed on the recording material due to a shortage of electric power, in a case where the turn-on duty ratio of a second heat generation member to a first heat generation member is switched, at a predetermined timing, in a direction in which the maximum amount of possible heat generation is decreased, with respect to the at least two heat generation members provided to the heat source, it is set as a condition that a turn-on ratio of the first heating member at the timing is smaller than a predetermined value.