A stage apparatus includes a first stage, a second stage movable in a first direction relative to the first stage, a sensor which reads a scale moving in the first direction together with the second stage and a sensor base which is formed from a material having a smaller thermal expansion coefficient than the first stage and fixes the sensor to the first stage. The sensor base is fixed to the first stage at two fixing positions located near a second axis having a second direction perpendicular to the first direction and passing through a specific position and sandwiching the specific position, and is fixed to the first stage at a fixing position located near a first axis having the first direction and passing through the specific position and the arrangement position of the sensor so as to be movable in the first direction.