A stage base includes a plate which supports a stage. The plate has a first structure and a second structure, and the first and second structures are coupled. The stage base further includes a component which is arranged on the plate and has a cooling unit, a coolant channel arranged to extend through the plate into the component, and a seal member arranged between the first structure and the second structure so as to surround the coolant channel, an interior and an exterior of the seal member being fastened with a fastener.