An image forming apparatus includes: a development device that develops an electrostatic latent image formed on a photosensitive drum into a toner image; a charger that charges the photosensitive drum; a development power supply that applies a prescribed bias voltage to the development device; an electric current measuring section that measures a development current flowing in the development device; and a calculating section that calculates a surface potential of the photosensitive drum based on the development current. The development device sequentially forms a plurality of image formation toner images on respective sheets of a recording medium. The image formation toner images each are a toner image for image formation. The electric current measuring section measures the development current in a period during which the image formation toner images are not formed.