The disclosed is a reference frequency generating device (11), which includes a GPS receiver (21), a PLL circuit (31), a detector (28), a memory unit (29), and a controller (22). The PLL circuit (31) controls the digitally controlled oscillator (26) based on a synchronizing control signal acquired based on a reference signal from the GPS receiver (21). The memory unit (29) stores a correspondence relation between a control value of the synchronizing control signal, and a voltage value and a temperature at that time. When the reference signal is not acquired, the controller 22 determines a holdover control signal based on the correspondence relation, and the voltage and temperature detected by the detector 28, and controls the digitally controlled oscillator (26).