To provide a gas-liquid treatment apparatus which solves such problem that a mixed gas prepared by a conventional steam apparatus has many chances to be exposed to outside air so that the gas is unstable, changed easily, and unreliable, prepares a mixed gas of high stability, and has low cost and high reliability.

A gas-liquid separation part 11 formed by a cooler and a liquid trap part 12 for collecting liquid are bonded by connection body 13 comprising a flange (the bottom plate of the separation part) 131 and a flange (the top plate of the trap part) 132 to be integrated.