A belt device includes an endless belt and a rotary driver contacting an outer circumferential surface of the belt to drive and rotate the belt. An opposed belt support is disposed opposite the rotary driver and in contact with an inner circumferential surface of the belt. A rotary belt support is disposed opposite the rotary driver via the opposed belt support and in contact with the inner circumferential surface of the belt. A belt support holder holds the opposed belt support and the rotary belt support to retain a predetermined interval between the opposed belt support and the rotary belt support. A biasing assembly presses against the belt support holder to move the opposed belt support and the rotary belt support collectively with respect to the rotary driver and bias the opposed belt support against the rotary driver.