An image forming apparatus includes a photosensitive drum, a developing section, a voltage applicator, a detector, a calculating section, and an evaluating section. The detector detects values of first and second currents. The first current flows between the photosensitive drum and the developing section during formation of an electrostatic latent image. The second current flows between the photosensitive drum and the developing section when the electrostatic latent image is not being formed. The calculating section calculates a toner charge-to-mass ratio. The evaluating section evaluates reliability of a calculation result of the toner charge-to-mass ratio by comparing the second current value to a reference value. The reference value is of a reference current flowing between the photosensitive drum and the developing section when the electrostatic latent image is not being formed, and indicates a current value detected after adjustment to at least one of the photosensitive drum and the developing section.