An image forming apparatus includes: a conveying path on which a recording medium is conveyed; an image capturer that includes a light source and radiates light from the light source to capture the recording medium being conveyed at different timings to generate at least two images including a first image and a second image; and a movement amount calculator that calculates a movement amount of the recording medium between capturing timings of the first and second images, wherein the movement amount calculator: calculates an index distance which is a distance in a conveying direction of a pattern formed by reflected light from the recording medium; calculates a ratio between the index distance and a reference distance used for comparison with the index distance; and calculates a movement amount of the recording medium between the capturing timings of the first and second images.