A mode-locked laser device includes a Fabry-Perot resonator, a mode-locking element disposed within the resonator, a solid-state laser medium disposed within the resonator, and exciting means for applying excitation light to the solid-state laser medium. The opposite ends of the resonator, the mode-locking element and the solid-state laser medium are disposed to provide an average beam diameter of lasing light of not more than 150 μm on the mode-locking element and an average beam diameter of the lasing light of not more than 200 μm within the solid-state laser medium.