An image forming apparatus includes: an image forming unit that performs image forming processing on a recording sheet; a primary central processing unit (CPU) and a secondary CPU, where the primary CPU receives a job externally and instructs the secondary CPU to monitor and control the image forming unit to perform the image forming processing; sensors that sense a state of the image forming unit and output sensor data indicating the state of the image forming unit, a first transceiver; and a second transceiver. The secondary CPU monitors the sensor data to generate diagnostic data. The first transceiver performs duplex communication with the primary CPU to send and receive data other than the diagnostic data. The second transceiver sends the diagnostic data to the diagnostic server without relaying via the primary CPU.