A steam turbine includes a rotor that rotates about an axis, a casing that covers the rotor from an outer side in a radial direction with respect to the axis, and a cover disposed outside the casing to form a hollow path portion between an outer peripheral surface of the casing and the cover, in which the cover is connected to a negative pressure source configured to put the path portion into a vacuum state, and the path portion is a space isolated from a space inside the casing.