The subject innovation is the field and relates to a digital controller which enables, even in remote, by adding a self-diagnostic function according to the digital MCU therein outside the normal operation whether the input program and a digital output point lamp the control of the conventional voltage switch there is a purpose to make him easily see through. After the subject innovation is the input power supply supplied from an external source to achieve this object characteristic, a digital input unit 11 to a photo-coupler (Photo Coupler) within the controller operation; Self-diagnosis performed by the self-test to check the operation state of the controller, the state of lighting display lamp (A) section 12; When the photo-coupler inside the controller to operate using the received input power, by being processed by the internal sequence (Internal Sequence), the sequence processor 13 for operating the indicators and a digital output; Digital logic gates to display and preventing the inflow of external noise, the operating status of the controller according to the digital input (14); And a digital output section 15 including a channel 17 delimited by the field (Local) and the far-field (SCADA); It includes. Automatic transfer switch voltage digital controllers, self-diagnostics, status indicator, digital logic gate, digital MCU