An optical writing device adopting a low cost and simple structure can obtain temperatures of light emitting elements. The device comprises a plurality of light emitting elements arranged linearly in a main scanning direction. The amount of light emitting of the light emitting elements changes by self-generated heat. The light emitting elements are divided into a plurality of groups. Each of the groups includes a prescribed number of light emitting elements. The device comprises a control unit for calculating the amount of heat generation of the light emitting elements for each of groups from clock time t0 to clock time t0+Δt. The control unit calculates the temperature for each of the groups at the clock time t0+Δt, based on the amount of heat generation from the clock time t0 to the clock time t0+Δt and the temperature at the clock time t0.