To eliminate various error factors so as to detect with high accuracy and high stability (repeatability), and execute at a low cost.

A capacitance type sensor is provided with a power source part 5 outputting constant positive voltage V and negative voltage -V, an integrating circuit 6 for integrating positive voltage V or negative voltage -V, a comparing circuit 7 with its output reversed when output voltage E of the integrating circuit 6 reaches the preset upper limit value Eu and lower limit value Ed, a first switch part 8 for imparting positive voltage V or negative voltage -V selectively to the integrating circuit 6 in correspondence with the output level of the comparing circuit 7, a second switch part 9 for connecting a detecting capacitor 2 or a correcting capacitor 3 as a constant of the integrating circuit 6 selectively to the integrating circuit 6, and a detection processing part 4 for switching the second switch part 9 periodically according to specified conditions and obtaining the grade of the physical quantity on the basis of a detection signal Sp outputted from the comparing circuit 7.