It is an object to provide a scanning-laser microscope apparatus and a light-amount detection unit that can perform quantitative observation by reporting to the operator the light intensity irradiating a specimen due to optical stimulation. There is provided a laser microscope apparatus including a stimulus optical system for irradiating a stimulus laser beam for applying a stimulus to a specific position of a specimen; a light detector for measuring the light intensity of the stimulus laser beam; a light-intensity correction circuit for correcting the measured value from the light detector; an integrating circuit for integrating the detected value from the light-intensity correction circuit; and a display device for displaying the detected integrated value from the integrating circuit.