An image forming apparatus includes an exposing section, a pulse generating section, a frequency storing section, an emission control section, a smoothing section, and a driving-current generating section. The pulse generating section generates a periodic pulse signal indicating light amount of light beam emitted by a light source of the exposing section. The frequency storing section stores in advance a plurality of frequencies of the pulse signal. The emission control section selects, in the rendering of each main scanning line, any one of the plurality of frequencies and instructs the pulse generating section to generate the pulse signal having the selected frequency. The smoothing section smoothes the pulse signal generated by the pulse generating section according to the instruction of the emission control section and generates analog signal. The driving-current generating section generates driving current for the light source of the exposing section on the basis of the analog signal.