A device for measuring floating micro-organisms, comprising: a first main body which has a first space portion and a second space portion defined by a plurality of walls (211, 213, 215, 217); a collecting portion for collecting the floating micro-organisms; a second main body which is spaced apart to a side of the first main body and in which the collecting portion for collecting the floating micro-organisms is installed; an air flow path which is formed between the first main body and the second main body and through which air including floating micro-organisms can flow; a light emitting unit which is installed in the first space portion and which is configured to emit a preset wavelength region of light toward the collecting portion; and a light receiving unit which is installed in the second space portion and which is configured to detect a fluorescence signal generated from light within the preset wavelength region which acts on riboflavin contained in the floating micro-organisms, wherein the light emitting unit, the collecting portion and the light receiving unit are arranged such that they provide a first path along which light emitted from the light emitting unit can pass and which extends from the light emitting unit to a point on the collecting portion, and a second path along which the fluorescence signal can pass and which extends from the point on the collecting portion to the light receiving unit, wherein the first path of light and the second path of the fluorescence signal intersect at the point on the collecting portion; wherein the plurality of walls (211, 213, 215, 217) includes a first wall and a second wall which define the first space portion, wherein the first wall defines a surface of the first space portion and the second wall defines the opposite surface of the first space portion, wherein a first lens is disposed on a light outlet side of the light emitting unit and in the first space portion, the first lens being configured to collect light emitted from the light emitting unit, wherein a first filter is provided on a side of the first lens and is disposed so that the preset wavelength region of light is passed through the first filter, and wherein the first filter is installed in the first space portion, characterized in that the device further comprises a spread preventing portion, said spread preventing portion being provided on an outlet side of the first filter and configured to prevent light scattering, wherein the spread preventing portion is formed such that the first wall after the first filter and along the first path is rounded and extended in the direction toward the point on the collecting portion such that a size of the first space portion is decreased toward the point on the collecting portion. a first main body which has a first space portion and a second space portion defined by a plurality of walls (211, 213, 215, 217); a collecting portion for collecting the floating micro-organisms; a second main body which is spaced apart to a side of the first main body and in which the collecting portion for collecting the floating micro-organisms is installed; an air flow path which is formed between the first main body and the second main body and through which air including floating micro-organisms can flow; a light emitting unit which is installed in the first space portion and which is configured to emit a preset wavelength region of light toward the collecting portion; and a light receiving unit which is installed in the second space portion and which is configured to detect a fluorescence signal generated from light within the preset wavelength region which acts on riboflavin contained in the floating micro-organisms, wherein the light emitting unit, the collecting portion and the light receiving unit are arranged such that they provide a first path along which light emitted from the light emitting unit can pass and which extends from the light emitting unit to a point on the collecting portion, and a second path along which the fluorescence signal can pass and which extends from the point on the collecting portion to the light receiving unit, wherein the first path of light and the second path of the fluorescence signal intersect at the point on the collecting portion; wherein the plurality of walls (211, 213, 215, 217) includes a first wall and a second wall which define the first space portion, wherein the first wall defines a surface of the first space portion and the second wall defines the opposite surface of the first space portion, wherein a first lens is disposed on a light outlet side of the light emitting unit and in the first space portion, the first lens being configured to collect light emitted from the light emitting unit, wherein a first filter is provided on a side of the first lens and is disposed so that the preset wavelength region of light is passed through the first filter, and wherein the first filter is installed in the first space portion, characterized in that the device further comprises a spread preventing portion, said spread preventing portion being provided on an outlet side of the first filter and configured to prevent light scattering, wherein the spread preventing portion is formed such that the first wall after the first filter and along the first path is rounded and extended in the direction toward the point on the collecting portion such that a size of the first space portion is decreased toward the point on the collecting portion.