Provided is a head cover structure of an engine, which is capable of increasing supporting rigidity of a head cover. The engine includes a driving force transmission mechanism for transmitting a driving force of a crankshaft to a valve train, in which the head cover includes a bulging portion for covering an upper side of the driving force transmission mechanism on one end side thereof in a cylinder row direction, and an engine mounting portion is attached to the bulging portion. The bulging portion is provided with an inclined surface portion having an inclined surface inclined downwardly toward the other end side in the cylinder row direction, and the inclined surface is formed to rise upwardly from an intermediate position in the cylinder row direction so as to be continuous with a top surface of the bulging portion on the one end side in the cylinder row direction.