a mos transistor the operating point of which in detecting the predetermined voltage is selected as the point at which the ratio of the current to the conductive constant of the mos transistor is above 0 1 the temperature compensation thereby achieved is good enough that the measured value almost coincides with the design value without the need of using a variable resistor application_number US 76359977 A description the object of this invention is to provide a new voltage detecting circuit which selects the operating point in the higher region of i k when the voltage detecting circuit detects which is able to make to temperature compensation and which is able to set the detected voltage at a predetermined value without adjusting a variable resistor referring now to the detailed description of the embodiments illustrated in the drawing fig1 is a circuit diagram showing an embodiment of the voltage detecting circuit according to the invention the fundamental circuit construction is similar to the conventional voltage detecting circuit as shown in fig1 the different point between the conventional voltage detecting circuit and the voltage detecting circuit according to this invention is the operating point of the mos transistor when the voltage detecting circuit detects accordingly the respective circuit elements ae identified by the same reference numerals as the corresponding circuit elements shown in fig1 in fig 10 t 4 is an n channel mos transistor connected between the power source terminal 1 and the voltage dividing circuit 3 the gate electrode of the n channel mos transistor t 4 receives the sampling pluse sp at the detecting time the sampling pulse sp is obtained from the dividing circuit dividing the oscillating frequency of the quartz crystal oscillating circuit for the.