The invention provides an image forming apparatus which can easily perform transfer adjustment and can realize good transfer control. In one embodiment, the image forming apparatus has a transfer member, a detector, a display, a transfer bias power source circuit, a memory, a processor, and so on. The processor calculates a value indicating a resistance value of a sheet, based on a measurement value of a voltage value or a current value of the transfer member by the detector. Further, when the calculated value indicating the resistance value of the sheet is a value outside a range of an allowable range stored in the memory, the processor makes the display display a message to recommend adjustment of a transfer bias to be applied to the transfer member by the transfer bias power source circuit.