A light sheet microscope (100; 200; 300; 800) comprising: an objective (7; 41); an illumination optical system (4; 31, 32, 33, 34, 35) that irradiates sample with a light sheet from a direction that is different from an optical axis direction of the objective (7; 41); first adjustment means for adjusting a relative position between a light sheet plane on which the light sheet is formed and the objective (7; 41) in the optical axis direction of the objective (7; 41); second adjustment means (6; 32) for adjusting a relative position between the light sheet plane and the sample in the optical axis direction of the objective; and a controller (20; 30; 40) that controls the first adjustment means on the basis of light that is from the light sheet plane and that is detected via the objective (7; 41) when a relative position between the light sheet plane and the sample is changed by the second adjustment means (6; 32), an image pickup device that has a light-receiving surface and that obtains an image of the sample via the objective (7, 41); characterized in that the light sheet microscope (100; 200; 300; 800) further comprises: a first light shielding plate (14; 43) that is arranged on a far side of a position and that has an opening, wherein the position is in an optical path branching from an optical path between the image pickup device and the objective (7, 41) and corresponds to the light-receiving surface; a second light shielding plate (16; 45) that is arranged on a near side of a position and that has an opening, wherein the position is in an optical path branching from an optical path between the image pickup device and the objective (7, 41) and corresponds to the light-receiving surface; a first photodetector that detects light that is from the light sheet plane and that passed through the first light shielding plate (14; 43), and a second photodetector that detects light that is from the light sheet plane and that passed through the second light shielding plate (16; 45), wherein the controller (20; 30; 40) is configured to control the first adjustment means on the basis of an output signal from the first photodetector and an output signal from the second photodetector. an objective (7; 41); an illumination optical system (4; 31, 32, 33, 34, 35) that irradiates sample with a light sheet from a direction that is different from an optical axis direction of the objective (7; 41); first adjustment means for adjusting a relative position between a light sheet plane on which the light sheet is formed and the objective (7; 41) in the optical axis direction of the objective (7; 41); second adjustment means (6; 32) for adjusting a relative position between the light sheet plane and the sample in the optical axis direction of the objective; and a controller (20; 30; 40) that controls the first adjustment means on the basis of light that is from the light sheet plane and that is detected via the objective (7; 41) when a relative position between the light sheet plane and the sample is changed by the second adjustment means (6; 32), an image pickup device that has a light-receiving surface and that obtains an image of the sample via the objective (7, 41); a first light shielding plate (14; 43) that is arranged on a far side of a position and that has an opening, wherein the position is in an optical path branching from an optical path between the image pickup device and the objective (7, 41) and corresponds to the light-receiving surface; a second light shielding plate (16; 45) that is arranged on a near side of a position and that has an opening, wherein the position is in an optical path branching from an optical path between the image pickup device and the objective (7, 41) and corresponds to the light-receiving surface; a first photodetector that detects light that is from the light sheet plane and that passed through the first light shielding plate (14; 43), and a second photodetector that detects light that is from the light sheet plane and that passed through the second light shielding plate (16; 45), wherein the controller (20; 30; 40) is configured to control the first adjustment means on the basis of an output signal from the first photodetector and an output signal from the second photodetector.