A spectrometer comprising: a first spectroscopic unit having a first light passing part, a first reflection part reflecting light passing through the first light passing part, a common reflection part reflecting the light reflected by the first reflection part, a first dispersive part dispersing and reflecting the light reflected by the first reflection part and reflected by the common reflection part, and a first light detection part detecting the light dispersed and reflected by the first dispersive part; and a second spectroscopic unit (2B, 2C) having a second light passing part (21B, 21C), a second reflection part (11B, 11C) reflecting light passing through the second light passing part (21B, 21C), the common reflection part reflecting the light reflected by the second reflection part (11B, 11C), a second dispersive part (40B, 40C) dispersing and reflecting the light reflected by the second reflection part (11B, 11C) and reflected by the common reflection part, and a second light detection part (22B, 22C) detecting the light dispersed and reflected by the second dispersive part (40B, 40C), the first light passing part, the first reflection part, the common reflection part, the first dispersive part, and the first light detection part are arranged along a first reference line extending in a first direction when viewed in an optical axis direction of the light passing through the first light passing part, and the second light passing part (21B, 21C), the second reflection part (11B, 11C), the common reflection part, the second dispersive part (40B, 40C), and the second light detection part (22B, 22C) are arranged along a second reference line extending in a second direction intersecting with the first reference line in the common reflection part when viewed in an optical axis direction of the light passing through the second light passing part (21B, 21C). a first spectroscopic unit having a first light passing part, a first reflection part reflecting light passing through the first light passing part, a common reflection part reflecting the light reflected by the first reflection part, a first dispersive part dispersing and reflecting the light reflected by the first reflection part and reflected by the common reflection part, and a first light detection part detecting the light dispersed and reflected by the first dispersive part; and a second spectroscopic unit (2B, 2C) having a second light passing part (21B, 21C), a second reflection part (11B, 11C) reflecting light passing through the second light passing part (21B, 21C), the common reflection part reflecting the light reflected by the second reflection part (11B, 11C), a second dispersive part (40B, 40C) dispersing and reflecting the light reflected by the second reflection part (11B, 11C) and reflected by the common reflection part, and a second light detection part (22B, 22C) detecting the light dispersed and reflected by the second dispersive part (40B, 40C), the first light passing part, the first reflection part, the common reflection part, the first dispersive part, and the first light detection part are arranged along a first reference line extending in a first direction when viewed in an optical axis direction of the light passing through the first light passing part, and the second light passing part (21B, 21C), the second reflection part (11B, 11C), the common reflection part, the second dispersive part (40B, 40C), and the second light detection part (22B, 22C) are arranged along a second reference line extending in a second direction intersecting with the first reference line in the common reflection part when viewed in an optical axis direction of the light passing through the second light passing part (21B, 21C).