A substrate processing apparatus includes a substrate holding part, a substrate rotating mechanism, and a chamber. The substrate rotating mechanism includes an annular rotor part disposed in an internal space of the chamber and a stator part disposed around the rotor part outside the chamber. The substrate holding part is attached to the rotor part in the internal space of the chamber. In the substrate rotating mechanism, a rotating force is generated about a central axis between the stator part and the rotor part. The rotor part is thereby rotated about the central axis, being in a floating state, together with a substrate and the substrate holding part. In the substrate processing apparatus, the substrate can be easily rotated in the internal space having excellent sealability. As a result, it is possible to easily perform single-substrate processing in a sealed internal space.