There is provided a substrate processing apparatus which supplies a processing gas onto a surface of a substrate on a substrate mounting table from a gas nozzle. The apparatus includes: a ring member installed in a leading end side of to the gas nozzle rather than a through-hole and including an inner peripheral surface on which the gas nozzle inserted into the through-hole is mounted, at least one of contours of an outer peripheral surface and the inner peripheral surface being set to a spiral curve or a polygon obtained by linearly approximating the curve; and a pedestal part on which the ring member is mounted at left and right positions spaced apart from each other in a circumference direction of the ring member. A height of a position at which the gas nozzle is supported by the ring member is adjusted with a rotation of the ring member.