An operation state display apparatus includes a counter for receiving input signals which respectively represent the individual operation states of a controlled object and for counting the duration time of at least one of the ON and OFF state of the input signal. A memory device is provided for memorizing the period of time lapse from an operation initiation reference time when the input signal goes from the OFF state to the ON state or vice versa. A display device is provided for displaying in the form of a time chart the operation state of the controlled object according to the data of the counter and of the memory device. The reference operation state of the controlled object can also be displayed on the display device.
