A Q-switch laser device for outputting a pulse laser from an optical resonator is equipped with a Q-switch for changing high/low values of a Q-value for the resonator; a switch-pulse generation means for generating a switch pulse with a frequency for determining a repetition period of the pulse laser; an RF oscillation means for generating an RF signal with a frequency higher than that of the switch pulse; a pulse synchronization means for inputting the switch pulse and RF signal and outputting a phase-synchronization pulse, where arising timing of the former is synchronized with a phase of the latter; and an RF modulation means for inputting the phase-synchronization pulse and outputting the RF signal as an RF modulation signal of the RF signal made ON/OFF, corresponding to a period of L/H-levels of an input pulse, wherein the Q-switch changes the Q-value of the resonator to the high/low values.