In a gas sensor assembling apparatus configured to integrate first and second gas sensor components, a posture adjustment part configured to adjust the posture of a first member in a horizontal plane adjusts the posture of the first member to an insertion possible posture determined in advance while holding the first member having been transferred from a conveyance mechanism at a posture adjustment position fixedly determined in advance, and transfers the first member in the insertion possible posture to the conveyance mechanism while maintaining at the posture adjustment position, the conveyance mechanism conveys, to an integration position, the first member in the insertion possible posture, and at the integration position, the first member and the second member are integrated with each other by inserting a sensor element of a second member into an insertion port of the first member in the insertion possible posture.