GAS MEASUREMENT ADAPTER

A gas measurement adapter (1) comprising: a flow tube portion (21) configured to allow gas to pass through the flow tube portion (21); and a window portion (31,31A) configured to allow measurement light for measuring a component of the gas passing through the flow tube portion (21) to pass through the window portion (31,31 A), wherein the window portion (31,31 A) is thinner than the flow tube portion (21) and is molded integrally with the flow tube portion (21), wherein the window portion (31) comprises an effective portion (32) configured to allow the measurement gas to pass through the effective portion (32) and an outer peripheral portion (33) provided on an outer periphery of the effective portion (32), an inner surface (50) of the window portion (31) being configured such that an outer perimeter (34) of the effective portion (32) is contiguously coplanar with the outer peripheral portion (33), or in that an outer perimeter (34A) of the window portion (31A) on an inner surface (52) of the window portion (31 A) is contiguously coplanar with a portion of the flow tube portion (21) bordering the outer perimeter (34A) of the window portion (31A).