A slit lamp microscope, comprising: a main illumination system that includes a first light source unit that outputs first light and a slit forming unit that forms a slit and illuminates an eye with the first light having passed through the slit; a background illumination system that includes a second light source unit that outputs second light, and illuminates, with the second light, a peripheral area of an area of the eye irradiated with the first light; an observation system that includes an eyepiece lens, an imaging device, and a group of optical elements that guides reflected light of the first light and reflected light of the second light from the eye to the eyepiece lens and the imaging device; and a controller that is configured to interlockingly control the main illumination system and the second light source unit, wherein the controller is configured to interlockingly control the first light source and the second light source, wherein the controller comprises an illumination condition specifying unit that analyzes pixel values of a photographed image acquired by the imaging device to specify an illumination condition; characterized in that the slit has a changeable width and the controller further comprises a control content determining part that determines control contents based on the illumination condition specified, wherein the controller is configured to interlockingly control the main illumination system and the second light source unit based on the control contents determined by the control content determining part, wherein the controller receives a control instruction to control the second light source unit and is configured to interlockingly control the first light source unit and the second light source unit based on contents of the control instruction, and wherein the first light source unit includes a first visible light source that outputs first visible light as the first light, the second light source unit includes a second visible light source that outputs second visible light as the second light, and when an instruction for changing intensity of the second visible light is received as the control instruction, the controller controls the second visible light source so as to change the intensity of the second visible light by a first change amount corresponding to the instruction and controls the first visible light source so as to change intensity of the first visible light by a second change amount corresponding to the first change amount. a main illumination system that includes a first light source unit that outputs first light and a slit forming unit that forms a slit and illuminates an eye with the first light having passed through the slit; a background illumination system that includes a second light source unit that outputs second light, and illuminates, with the second light, a peripheral area of an area of the eye irradiated with the first light; an observation system that includes an eyepiece lens, an imaging device, and a group of optical elements that guides reflected light of the first light and reflected light of the second light from the eye to the eyepiece lens and the imaging device; and a controller that is configured to interlockingly control the main illumination system and the second light source unit, wherein the controller is configured to interlockingly control the first light source and the second light source, wherein the controller comprises an illumination condition specifying unit that analyzes pixel values of a photographed image acquired by the imaging device to specify an illumination condition; characterized in that the slit has a changeable width and the controller further comprises a control content determining part that determines control contents based on the illumination condition specified, wherein the controller is configured to interlockingly control the main illumination system and the second light source unit based on the control contents determined by the control content determining part, wherein the controller receives a control instruction to control the second light source unit and is configured to interlockingly control the first light source unit and the second light source unit based on contents of the control instruction, and wherein the first light source unit includes a first visible light source that outputs first visible light as the first light, the second light source unit includes a second visible light source that outputs second visible light as the second light, and when an instruction for changing intensity of the second visible light is received as the control instruction, the controller controls the second visible light source so as to change the intensity of the second visible light by a first change amount corresponding to the instruction and controls the first visible light source so as to change intensity of the first visible light by a second change amount corresponding to the first change amount.