The Colpitts circuit is configured so that an equivalent capacitance of the voltage-dividing first and second capacitors connected in series through the output of the transistor amplifier is variable under the condition that the ratio of the capacitance of the first capacitor to that of the second capacitor is kept unchanged at a prescribed value. The first and second capacitors are, as a whole, configured as a matrix of elemental capacitors with 2 rows and a plural number n of columns, an array of the elemental capacitors in the first row being allotted to the first capacitor and an array of the elemental capacitors in the second row being allotted to the second capacitor. Two elemental capacitors in each column j (j=1, 2, . . . n) are connected in series and the ratio of the capacitance of the elemental capacitor corresponding to the 1j element of the matrix to the capacitance of the elemental capacitor corresponding to the 2j element has the prescribed value. The Colpitts circuit further has a first switch and a second switch allotted to each of the columns. Each of the elemental capacitors allocated to the first row is connected to the control electrode of the transistor amplifier through the first switch, and the junction of the two elemental capacitors allocated to each column is connected to the output of said transistor amplifier through the second switch. The first and second switches are operated synchronously for every column.