To eliminate erasing of a written image desired to be stored contrary to intention by carelessly operating an erasing switch in a writing board such as an electronic blackboard for erasing the image on a writing sheet by operating an automatic eraser by operating the switch.

An erasing switch 40 is connected together with an automatic erasing unit 30 to a control means 35, and the unit 30 is started when operation of the switch 40 for a set time or longer is sensed by the means 35. When copying of a written image is, for example, desired, even if the switch 40 is erroneously pushed once, the unit 30 is not operated only by it, but as long as the switch 40 is not continuously operated for a set time or more, it prevents erroneous erasing of the image.