PURPOSE: To form a modulator with excellent modulation distortion factor and to increase the lock range of a PLL type modulator by inserting a leakage resistance to a phase/frequency detector provided with a conventional charge pump.

CONSTITUTION: In order to expand the lock range, the phase/frequency comparator (PFC) 101 is used and a leakage resistor 102 is used for the output of the charge pump of the PFC is inserted to eliminate a dead band so as not to bring the output into a high impedance forcibly even at locking thereby improving the distortion factor. Even when the leakage resistor 102 is given to the charge pump output of the PFC 101, the function as a frequency comparator is not lost. Since a pulse having a pulse width proportional to the phase difference is generated at the lock state, the dead band is eliminated in the phase comparison characteristic and almost saw-tooth wave-shaped phase comparison characteristic is provided so as to improve the distortion factor remarkably.