An image forming apparatus includes an endless belt to rotate, belt rollers including a tension roller and an adjustment roller extending inside the endless belt, a nip roller extending adjacent the endless belt to form a nip between the nip roller and the endless belt, and a cam shaft that includes a nip forming cam and a tension adjustment cam. The nip forming cam moves the nip roller between a pressed position in which the nip roller is pressed against the endless belt, and a retracted position in which the nip roller is retracted from the endless belt. The tension adjustment cam moves the adjustment roller relative to the tension roller.