The invention provides a valve characteristic controller and a valve characteristic control system. When a valve timing is held, even if a Duty value of an operational signal of a variable valve timing controller (20) is slightly changed, a holding unresponsive range will be arisen. In the unresponsive range, a variation speed of the valve timing is very small. As temperature is decreased, the unresponsive range is extended and an individual difference becomes notable. While the valve timing is held, a computer (40) learns a deviation amount of a response characteristic of the valve timing based on a variation speed of the valve timing when the Duty value is slightly changed from the holding unresponsive range to outside thereof.