PURPOSE: To provide a digital image forming device capable of automatically making a stable developing action adjustment by recognizing the proper developing state of the device with a binary output neural network via software.

CONSTITUTION: This digital image forming device is provided with a state quantity detecting means (sensor or circuit) 3 detecting the state quantities (photoreceptor drum surface potential, P sensor pattern density) related to the controlled quantities (grid output voltage value, lamp output voltage value, or LD output current value, developing bias output voltage value) of the control subject (stuck developing toner) arranged in the device, a data storing means (RAM) 6 storing the controlled quantities, state quantities, and arithmetic data, a program storing means (ROM) 7 storing the control program controlling the controlled quantities, and an arithmetic processing means (CPU) 1 making arithmetic processing with the control program. The control program estimates the developing state with a binary output neural network.