A thermal mass flow sensor 10 enclosed airtightly in a sealed container 11 under an inert atmosphere for the purpose of suppressing disappearance of a coating layer on sensor wires 13a and 13b in association with use at a high temperature, further comprises an air release pipe 16 that is a pipe which brings an internal space and outside of the sealed container 11 in airtight communication with each other through an air release hole 16a that is a through-hole formed in an outer wall of the sealed container 11. An end of the air release pipe 16 on an opposite side to the air release hole 16a is sealed by plastic deformation to form a sealed part 16b. Thereby, after forming the sealed container 11 under a normal atmosphere, the internal space of the sealed container 11 can be closed airtightly. The sealed part 16b may be further sealed by welding. The sealed container 11 can be assembled easily and accurately in this way, and degradation in airtightness of the sealed container 11 in association with use at a high temperature can be suppressed.