A flow measurement device is disclosed, in which an accumulation of pollution substance onto a detection element is prevented, and which can measure a reverse flow similarly to a normal flow. On both ends of an outer wall 23 outer peripheral portion of a divided flow pipe 20 having a &OHgr;-shape pipe passage, there are oppositely formed an inlet port 25 and an outlet port 26, which open in faces orthogonal to a flow direction of a main flow M that is a detection object. Within the divided flow pipe 20, by a curved partition 27, plural branch flow passages 28a, 28b mutually branching and joining in the divided flow pipe 20 are formed. Inside both end portions of the outer wall 23, undulation portions 32, 33 are formed so as to clog an inlet and an outlet of the outer peripheral side branch flow passage 28a and, by this, throttles are formed respectively in a flow passage between the inlet port 25 and the inlet of the branch flow passage 28a and a flow passage between the outlet port 26 and the outlet of the branch flow passage 28a. In a bottom portion of the outer wall 23 of the divided flow pipe 20, a detection element 31 is attached so as to be exposed to a flow in the outer peripheral side branch flow passage 28a and, against its detection face, a down flow DW further divided from a divided flow D obliquely impinges.