To raise pressure resistance of a first housing 2A which receives pressure by secondary molding as a primary mold product when secondary molding is performed to a second housing 2B in a flow measurement device 1.

The flow measurement device 1 includes: the first housing 2A for forming a bypass flow channel; and the second housing 2B which is formed by secondary molding by using the first housing 2A as a primary mold product. In addition, the second housing 2B has a hollow part 7 inside of which the bypass flow channel is formed, and on the outer peripheral surface of the first housing 2A, a recess 26 which dents to the inside of the first housing 2A is provided on the upper side of the hollow part 7. Thus, a part of a mold M for holding the first housing 2A is inserted into the recess 26 in the secondary molding, and a mold press area of the first housing 2A to be supported by the mold M in the secondary molding is increased.