The present invention aims at attaining a liquid surface level detecting apparatus, which can be used in various detection targets and usage environments without selecting a detection target, can efficiently irradiate a light to a liquid surface level detecting unit and detect a variation in a light reception amount of a light receiving means at a high sensibility, and can be excellent in durability, easy to manufacture, and be actually used. By placing a light shielding means 14 so as not to directly irradiate the light from a light emitting means 12 to a light receiving means 13, the light from the light emitting means is scattered by an optically scattering means 16, and a part of that scattering light is radiated to an outside by the liquid surface level detecting unit on a light radiating means (an optically transmitting member) 11. On the other hand, the scattering light, which is reflected without being radiated, is received by the light receiving means, and the change in that light reception amount is detected. Consequently, if a liquid 17 exists in the outside, a light amount, which is reflected by a boundary between the liquid and the light radiating means and returned to an inside of the light radiating means, is reduced, and the light reception amount in the light receiving means is also reduced. Thus, by measuring the change in the light reception amount, it is possible to detect a liquid surface level of the liquid.