An oscillation circuit has a first inverter connected to an external piezoelectric resonator, a first feedback resistor disposed between input/output terminals of the first inverter, first/second variable capacitive elements connected to input/output of the first inverter, a charging circuit supplying input/output terminal with a reference current to charge the capacitive element, a comparator comparing a charging voltage of input/output with a reference voltage, and a control circuit that, in a calibration operation, at a first time, causes the charging circuit to start supply the reference current to the input terminal or the output terminal, and, at a second time after the first time, generates the control signal for setting a capacitance value of the first or second variable capacitive element so that the charging voltage becomes close to the reference voltage according to a comparison result of the comparator.