Electric motor, rotary drive system, and hydraulic excavator

An electric motor includes a rotor, a stator, and an electric motor casing. The electric motor casing forms a first accommodating space accommodating a rotary shaft and a rotor core and a stator, and has an inner peripheral surface including an abutting inner peripheral surface in contact with a top portion on the radially outer side of a core convex portion. An outer peripheral-side flow path through which a cooling medium is capable of flowing is formed between the core convex portions adjacent to each other in the peripheral direction. The outer peripheral-side flow path is defined by an outer peripheral surface of the core main body and the inner peripheral surface of the electric motor casing.