JPH0525288B

PURPOSE:To obtain a small-sized detector having high reliability regardless of the kind of a container receiving an object, by allowing an electromagnetic wave or ultrasonic wave variable in an expanse angle to be incident to an object and detecting the state of the object on the basis of the intensity of the reflected wave from the object. CONSTITUTION:When an electromagnetic wave is allowed to be vertically incident to the surface of a liquid 4 from a light source 2, the intensity I of the reflected light thereof is inversely proportional to the square of the distance L up to the surface of the liquid 4. By this, the reflected light incident to a photodetector 6 is taken out as a photocurrent to be converted to signal voltage and, when this voltage value coincides with a predetermined reference voltage value, it is judged that the distance L becomes a predetermined reference distance L0 and it can be decided that the liquid in a tank becomes a predetermined residual amount. Further, a light projecting lens 3 is moved with respect to the light source 2 and, by regulating the interval (a) between both of them, the expanse angle theta of emitted luminous flux can be set arbitrarily. By this, the intensity I of the reflected light can be made same regardless of the kind of the tank and, when the voltage value becomes the predetermined reference voltage value, it can be judged that the residual amount of the liquid becomes a predetermined value, without regulating the reference voltage value at all.