An image forming apparatus includes an image forming unit, a first detector including a first light emitting device, a first mixed-light receiving device and a first diffuse reflection light receiving device, a second detector including a second light emitting device and a second mixed-light receiving device, and a concentration correction unit. The first mixed-light receiving device detects a mixed light including regular and diffuse reflection light reflected from a transport member. The first diffuse reflection light receiving device detects the diffuse reflection light. The second mixed-light receiving device detects the mixed light. The concentration correction unit conducts concentration correction using detection results of the first and second detectors. A first correction pattern reflecting the regular and diffuse reflection light and detectable by the first detector and a second correction pattern reflecting only the regular reflection light and detectable by the second detector are formed different positions on the transport member.