A solid laser apparatus has either a combination of a lowpass filter (9c) and a highpass filter (9d) or a bandpass filter 9f provided in its output control circuit (8, 9, 10) for increasing the gain and adjusting the phase of a signal in the vicinity of the relaxation oscillating frequency.Also, a solid laser apparatus has the phase shift circuit (9g) provided in its output control circuit (8,9,10) for advancing the phase of a signal in the vicinity of the relaxation oscillating frequency thereof.Moreover, a solid laser apparatus has a pseudo notch filter (9h), which is arranged for the gain to have a local minimum at the relaxation oscillating frequency of the solid laser apparatus, provided in the output control circuit (8,9,10) so that the peak of the gain transmission characteristic of the nonlinear optical device (4) or of a combination of the nonlinear optical device (4) and the microchip laser crystal (3) is offset.