An image forming apparatus includes: an image carrier on which an electrostatic latent image is to be formed; a rotary development unit having a plurality of developer carriers that carry a developer used for developing the electrostatic latent image, the developer including toner, the plurality of the developer carriers being sequentially moved to a development position opposing to the image carrier, to switch a development color; and a toner concentration detection unit that detects the concentration of toner of the developer carried by one of the developer carriers located at the development position.