A laser printer is provided printing with a high precision simply and at a high speed, and the laser printer uses a semiconductor laser which can vary the diameter of the emitted light while the light density is held constant. In the laser printer, laser rays emitted from a semiconductor laser are irradiated onto a photoconductor to vary its surface potential to produce a charge pattern particles adhere, and printing is performed by transferring the changed particles to a printing object. The semiconductor laser has a plurality of waveguide type resonators, the emitted beams of the resonators having a spatial superposition, and light emission is possible so that the emitted beams of the resonators having a spatial superposition with respect to each other among the resonators of the semiconductor laser are not substantially superimposed in time.