To measure the profile of the foaming plane of a foamable liquid and level thereof by picking up the image of a light beam projected through any one inspection window at the reflecting point on the liquid level, processing the image thus picked up and measuring the liquid level based on the position of the reflecting point on the image.

A camera 2 and a projector 3 are disposed in the direction for viewing the liquid level in a tank 1 through an inspection window 5 and the image of a light beam 3a projected from a projector 3 at the reflecting point on the liquid level 4a, 4b. When the light beam 3a reflects on the liquid level 4a at position (a) to form a reflecting point A, it is picked up as a bright point in the view field of the camera 2 and image data are obtained. When the liquid level is located at position (b), image of a reflecting point B is picked up. Since one and one correspondence is present between the liquid level and the coordinates (x, y) of the bright point being picked up as reflecting points A, B and displayed on the image, liquid level can be determined from the coordinates (x, y).