An image forming apparatus includes a sensor, an operation section, a controller, and a communication section. The sensor detects a sensor target. The operation section receives an operation instruction. The controller adjusts a sensitivity level of the sensor. The communication section transmits an instruction signal and a reception signal to an external device and receives an adjustment instruction from the external device. The instruction signal indicates an instruction for sensitivity level adjustment for the sensor. The adjustment instruction is an instruction as to whether or not to adjust the sensitivity level based on the instruction signal and the reception signal. The reception signal includes first information indicating time of detection signal reception by the controller receives the detection signal within a specific time period and second information indicating whether the operation section receives the operation instruction. The controller adjusts the sensitivity level of the sensor according to the adjustment instruction.