Provided is an image generation device that generates a specimen image that shows a specimen. The image generation device includes: a laser light source unit that emits laser light; a conversion unit that converts the laser light into combined light obtained by combining reflection light that is generated by reflection from the specimen and reference light that is generated by modulating a phase of the laser light; a first signal generation unit that generates a first detection signal corresponding to a light amount of the combined light; and an image generation unit that generates the specimen image. The conversion unit includes a modulation part that modulates the phase so as to cause periodical changes in the light amount of the combined light. The first detection signal contains a signal component that represents a turn of the periodical changes from increase to decrease. The image generation unit generates the specimen image using the signal component.