An image forming apparatus includes a belt, an image bearing member, a developing portion, a belt transfer portion, a steering roller, a detection portion, a cleaning blade, a control portion, and an instruction input portion. In a case where the input has been performed through the instruction input portion, the control portion executes, before starting image formation for the first time after replacement of the belt, an adjustment mode including a series of processes in which a relationship between the position in the width direction and the amount of tilting of the steering roller is adjusted, and also performs a toner supplying operation of supplying toner by transferring a toner image for supplying toner onto the belt.

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