A drive transmitter includes an internally toothed gear, a first support shaft to rotatably support the internally toothed gear without using a bearing, a drive source to apply a driving force to the internally toothed gear, a rotary body to which the driving force is transmitted via the internally toothed gear, and a grease retainer disposed on the first support shaft and to retain grease on at least one of a portion of the first support shaft facing the internally toothed gear and a portion of the internally toothed gear facing the first support shaft. An image forming apparatus includes the drive transmitter.