An object of the present invention is to provide an image forming apparatus and a method for forming an image that are capable of controlling the consumption of opposite polarity particles and suppressing the reduction of toner charge amount due to the carrier deterioration and can form high quality images over a long period of time even in the case where large quantities of images with small image area ratio are printed. The image forming device comprises a developer including the opposite polarity particles, a developer carrying member, a toner carrying member, and a voltage applying section for applying bias voltage overlapped with alternating current between the toner carrying member and the image carrying member, wherein the bias voltage overlapped with alternating current is a vibrating waveform including a trapezoidal wave, or a vibrating waveform in which a blank is inserted during application of a reverse development side voltage component.