A flow rate measurement device comprising: a housing including an inlet port and a discharge port for a fluid, which are formed to face each other; a rotating portion including a rotating shaft arranged perpendicularly to a virtual line C connecting the inlet port and the discharge port inside the housing, and a blade rotated by a flow of the fluid around the rotating shaft; a sensor portion arranged to be spaced apart from the rotating shaft in a radial direction of the rotating shaft so as to sense a number of rotations of the rotating portion; wherein the sensor portion includes a first sensing portion and an interaction portion; wherein the first sensing portion includes a first light emitting portion that generates light in an axial direction of the rotating shaft, and a first light receiving portion that is spaced apart from the first light emitting portion in the axial direction of the rotating shaft to receive the light emitted from the first light emitting portion and wherein the interaction portion provides interaction between the rotating portion and the first sensing portion and a control portion that measures a flow rate of the fluid on the basis of the number of rotations of the rotating portion sensed by the sensor portion, wherein the housing includes: a lower housing including the inlet port and the discharge port which are formed to face each other, and an opening on an upper side; and an upper housing coupled with the lower housing to cover the opening of the lower housing, and exposing a display portion of the control portion to outside, a sub-housing installed within the lower housing and supporting the rotating portion, and including a guide flow path formed to guide the fluid introduced through the inlet port toward the discharge port, and an opening on an upper side; and a cover member that covers the opening of the sub-housing and includes a first transparent guide groove protruding upward to guide the rotation of the interaction portion, wherein the first light emitting portion and the first light receiving portion are installed to face each other with respect to the first transparent guide groove. a housing including an inlet port and a discharge port for a fluid, which are formed to face each other; a rotating portion including a rotating shaft arranged perpendicularly to a virtual line C connecting the inlet port and the discharge port inside the housing, and a blade rotated by a flow of the fluid around the rotating shaft; a sensor portion arranged to be spaced apart from the rotating shaft in a radial direction of the rotating shaft so as to sense a number of rotations of the rotating portion; wherein the sensor portion includes a first sensing portion and an interaction portion; wherein the first sensing portion includes a first light emitting portion that generates light in an axial direction of the rotating shaft, and a first light receiving portion that is spaced apart from the first light emitting portion in the axial direction of the rotating shaft to receive the light emitted from the first light emitting portion and wherein the interaction portion provides interaction between the rotating portion and the first sensing portion and a control portion that measures a flow rate of the fluid on the basis of the number of rotations of the rotating portion sensed by the sensor portion, wherein the housing includes: a lower housing including the inlet port and the discharge port which are formed to face each other, and an opening on an upper side; and an upper housing coupled with the lower housing to cover the opening of the lower housing, and exposing a display portion of the control portion to outside, a sub-housing installed within the lower housing and supporting the rotating portion, and including a guide flow path formed to guide the fluid introduced through the inlet port toward the discharge port, and an opening on an upper side; and a cover member that covers the opening of the sub-housing and includes a first transparent guide groove protruding upward to guide the rotation of the interaction portion, wherein the first light emitting portion and the first light receiving portion are installed to face each other with respect to the first transparent guide groove. a lower housing including the inlet port and the discharge port which are formed to face each other, and an opening on an upper side; and an upper housing coupled with the lower housing to cover the opening of the lower housing, and exposing a display portion of the control portion to outside, a sub-housing installed within the lower housing and supporting the rotating portion, and including a guide flow path formed to guide the fluid introduced through the inlet port toward the discharge port, and an opening on an upper side; and a cover member that covers the opening of the sub-housing and includes a first transparent guide groove protruding upward to guide the rotation of the interaction portion, wherein the first light emitting portion and the first light receiving portion are installed to face each other with respect to the first transparent guide groove.