A substrate processing apparatus includes a chamber, a substrate holder, a camera, and a controller. The substrate holder holds a substrate in the chamber. The camera captures an image of an imaging region including the monitoring target in the chamber, and generates captured image data. The controller specifies an environmental state in an imaging region, monitors the state of the monitoring target based on the captured image data in a first determination procedure corresponding to a first environmental state when the environmental state is in the first environmental state, and monitors the state of the monitoring target based on the captured image data in a second determination procedure corresponding to a second environmental state and different from the first determination procedure when the environmental state is the second environmental state different from the first environmental state.