To make exactly detectable the surface level of a moving liq. by making flat a contact part of a detecting member in contact with the surface of the liq. and notching the end of the contact part on the upstream side in the moving direction of the liq. to form a releaf.

A detecting member 10 is brought into contact with the surface of a moving liq. 20 and moved to follow up the liq. level variation. When a core 14 provided on the opposite side through a rotary arm 13 moves, the change of voltages generated across sec. coils 17a, 17b is measured to detect the liq. level. A contact part 10a in contact with the surface of the liq. 20 is made flat, and the end of the contact part 10a on the upstream side in the moving direction of the liq. 20 is notched to form a releaf 10b, and the end 10c of the contact part 10a on the downstream side in the moving direction of the liq. 20 is made acute. This avoids depressing the sensing member 10 when the moving liq. 20 collides against the end of the contact 10a at the upstream of the liq. 20, resulting in a smooth flow of the liq. 20 under the contact part 10a.