PURPOSE: To reproduce a transmission clock of a digital data signal included in a digital modulation signal with high accuracy.

CONSTITUTION: The device is provided with band pass filters 40a, 40b, having both a high pass characteristic with an inverted frequency characteristic nearly to a frequency characteristic of a base band signal outputted from an orthogonal demodulation section and a low pass characteristic to eliminate a spurious component of a clock frequency of a digital data signal included in the base band signal. A square signal of the base band signal passing through the filters is calculated, a phase signal obtained by multiplying the calculated square signal by a reference clock signal having a frequency almost equal to a clock frequency is integrated over a prescribed measurement time and a reproduction clock of the digital data signal is calculated by using the integration value and the reference clock signal.