An image forming apparatus of the invention holds a first developing agent of a first color and inverse transfer preventing agent, supplies the first developing agent with predetermined potential, supplies the first developing agent to an image portion of an image carrier, supplies the inverse transfer preventing agent with the first developing agent and electric charge of an inverse polarity, supplies the inverse transfer preventing agent to a non-image portion having a predetermined potential difference relative to an image portion, brings the image carrier into contact with a transfer object medium to which a second developing agent of a second color different from the first color is already transferred and transfers the first developing agent to the transfer object medium.