A flow-velocity measuring device comprising: a main body having two end portions provided in a longitudinal direction of the main body; an inlet port formed on a front surface of the main body and opening toward the upstream of a measured fluid; an introducing channel being a flow channel and extending in the main body from the inlet port; a branch channel being a flow channel branched from the introducing channel and connected at a terminal end thereof to a first discharge port opening on a rear surface of the main body; a discharge channel extending from the introducing channel and connected at a terminal end thereof to a second discharge port opening on the rear surface of the main body; and a sensor element provided in the branch channel or in a measuring channel further branched from the branch channel and connected at a terminal end thereof to a third discharge port opening on the rear surface of the main body, wherein the main body comprises a front half member having the front surface and a rear half member having the rear surface, wherein the two half members (3, 4) are joined to each other along joint surfaces thereof such that the main body has a thickness between the front and rear surface; wherein the inlet port is provided on the front surface of the front half member near one end portion of the end portions of the main body and the first to third discharge ports are provided on the rear surface of the rear half member near the one end portion; the flow channels (14, 15) other than the discharge channel being defined by grooves formed on the joint surfaces of the front and rear half members (3, 4); and the discharge channel having an overlapped portion in which the discharge channel overlaps, in a direction of the thickness between the front and rear surface of the front and rear half members, the channel (15; 16) where the sensor element is provided, being a lateral hole which extends from an opening on a side surface of the corresponding half member in parallel with the joint surface of the half member, and being exclusively in communication with the introducing channel in an inner portion of the main body. a main body having two end portions provided in a longitudinal direction of the main body; an inlet port formed on a front surface of the main body and opening toward the upstream of a measured fluid; an introducing channel being a flow channel and extending in the main body from the inlet port; a branch channel being a flow channel branched from the introducing channel and connected at a terminal end thereof to a first discharge port opening on a rear surface of the main body; a discharge channel extending from the introducing channel and connected at a terminal end thereof to a second discharge port opening on the rear surface of the main body; and a sensor element provided in the branch channel or in a measuring channel further branched from the branch channel and connected at a terminal end thereof to a third discharge port opening on the rear surface of the main body, wherein the main body comprises a front half member having the front surface and a rear half member having the rear surface, wherein the two half members (3, 4) are joined to each other along joint surfaces thereof such that the main body has a thickness between the front and rear surface; a front half member having the front surface and a rear half member having the rear surface, wherein the two half members (3, 4) are joined to each other along joint surfaces thereof such that the main body has a thickness between the front and rear surface; wherein the inlet port is provided on the front surface of the front half member near one end portion of the end portions of the main body and the first to third discharge ports are provided on the rear surface of the rear half member near the one end portion; the flow channels (14, 15) other than the discharge channel being defined by grooves formed on the joint surfaces of the front and rear half members (3, 4); and the discharge channel having an overlapped portion in which the discharge channel overlaps, in a direction of the thickness between the front and rear surface of the front and rear half members, the channel (15; 16) where the sensor element is provided, being a lateral hole which extends from an opening on a side surface of the corresponding half member in parallel with the joint surface of the half member, and being exclusively in communication with the introducing channel in an inner portion of the main body.