PURPOSE: To prevent manipulating operation for a plant from being delayed and also prevent plant equipment from being broken or deteriorating in life owing to the delay of the manipulating operation by displaying trend graphs before and after alarm generation if an alarm is generated, and then instantaneously confirming the change state of a process value before the alarm generation and predicting process value variation after the alarm generation.

CONSTITUTION: Process values outputted by sensors provided at respective parts of a power generation plant to be monitored are inputted and a trend screen is displayed on a CRT device 4; when an inputted process value reaches a previously set alarm value, an alarm screen showing trend graphs before and after alarm generation is displayed on the CRT 4 to make an operator estimate the generation cause of the alarm, etc., and perform optimum manipulating operation.