PURPOSE: To make it possible to perform continuous measurement of wave surface, by providing image sensor devices, which perform specified operations based on measured data of the lengths of the parts of a plurality of measuring needles, which are not immersed in the water, and the interval between the measuring needles, and perform the operations concerning the dislacement and inclination of each wave surface.

CONSTITUTION: Periods are recorded by image sonsor 5a and 5b by using measuring meters 1aW1e and 2aW2e. The data recorded on video tape are reproduced and analyzed. When measuring needles and the image sensors are mounted on a common moving table and moved, the measurement of the encountered waves can be performed.