A scanning microscope (200, 300, 400, 500, 600, 700) comprising: a collecting lens (207, 608) that takes in a detection light from a sample; a focal position adjustment unit (205, 206, 220, 230, 240, 410, 510, 620) that moves in an optical axis direction of the collecting lens (207, 608) together with the collecting lens (207, 608) to make the collecting lens (207, 608) move in the optical axis direction; a detector (211, 303, 611) positioned at a location that is optically conjugate to a pupil of the collecting lens (207, 608); and a relay optical system (210, 222, 302, 411, 610, 622) that relays the pupil of the collecting lens (207, 608) to the detector, wherein the relay optical system (210, 222, 302, 411, 610, 622) includes: a first optical element (222, 411, 622) having a positive power, the first optical element (222, 411, 622) being positioned in the focal position adjustment unit (205, 206, 220, 230, 240, 410, 510, 620) and converting the detection light that was converted by the collecting lens (207, 608) into a parallel light flux, into a convergent light flux to be emitted outside of the focal position adjustment unit (205, 206, 220, 230, 240, 410, 510, 620); and a second optical element (210, 302, 610) that is positioned outside of the focal position adjustment unit(205, 206, 220, 230, 240, 410, 510, 620) and between the detector (211, 303, 611) and the first optical element (222, 411, 622). a collecting lens (207, 608) that takes in a detection light from a sample; a focal position adjustment unit (205, 206, 220, 230, 240, 410, 510, 620) that moves in an optical axis direction of the collecting lens (207, 608) together with the collecting lens (207, 608) to make the collecting lens (207, 608) move in the optical axis direction; a detector (211, 303, 611) positioned at a location that is optically conjugate to a pupil of the collecting lens (207, 608); and a relay optical system (210, 222, 302, 411, 610, 622) that relays the pupil of the collecting lens (207, 608) to the detector, wherein the relay optical system (210, 222, 302, 411, 610, 622) includes: a first optical element (222, 411, 622) having a positive power, the first optical element (222, 411, 622) being positioned in the focal position adjustment unit (205, 206, 220, 230, 240, 410, 510, 620) and converting the detection light that was converted by the collecting lens (207, 608) into a parallel light flux, into a convergent light flux to be emitted outside of the focal position adjustment unit (205, 206, 220, 230, 240, 410, 510, 620); and a second optical element (210, 302, 610) that is positioned outside of the focal position adjustment unit(205, 206, 220, 230, 240, 410, 510, 620) and between the detector (211, 303, 611) and the first optical element (222, 411, 622). a first optical element (222, 411, 622) having a positive power, the first optical element (222, 411, 622) being positioned in the focal position adjustment unit (205, 206, 220, 230, 240, 410, 510, 620) and converting the detection light that was converted by the collecting lens (207, 608) into a parallel light flux, into a convergent light flux to be emitted outside of the focal position adjustment unit (205, 206, 220, 230, 240, 410, 510, 620); and a second optical element (210, 302, 610) that is positioned outside of the focal position adjustment unit(205, 206, 220, 230, 240, 410, 510, 620) and between the detector (211, 303, 611) and the first optical element (222, 411, 622).