Disclosed is an image forming apparatus capable of preventing a paper jam in an arc-shaped sheet passing path for turning around a sheet and transporting the sheet in a double-sided transporting path. In this apparatus, a double-sided sheet passing path is formed so as to include: an arc-shaped interval that causes the sheet to turn around and to be transported to a registration sensor on an upstream side in the transport direction of a sheet and that includes the registration sensor as one end point; and an interval that transports the sheet having passed between ADU transport rollers, obliquely downward. A single-sided sheet passing path is formed so as to include an interval that transports the sheet having passed over the registration sensor in a substantially horizontal direction.