An image forming apparatus includes an image bearing member, a toner image forming unit, a sensor, and a control unit. The toner image forming unit is configured to form a toner image on the image bearing member. The sensor includes a light-emitting unit for emitting light, a light-receiving unit for receiving reflected light, an electrical circuit board in which the light-emitting unit is attached, and a frame supporting the electrical circuit board with the electrical circuit board bonded with three supporting portions. The sensor is configured to detect the toner image formed on the image bearing member. The control unit is configured to control a toner image forming condition of the toner image forming unit according to an output of the sensor.