The electromagnetic frictional engagement apparatus includes a housing member in which a housing space is formed, a clutch portion that couples the housing member in a disengageable manner to a shaft disposed so as to be rotatable relative to the housing member, and an electromagnetic coil that generates a magnetic force that actuates the clutch portion. The clutch portion has an outer clutch plate and an inner clutch plate that forms a magnetic path for a magnetic flux generated by the electromagnetic coil. Lubrication grooves through which a lubricant flows are formed in the inner clutch plate. Among the lubrication grooves, the total of groove areas of a portion of the lubrication grooves that is included in the magnetic path is 90 to 110% of a maximum lubrication groove area, so that magnetic flux density resulting from saturation of the magnetic path with magnetic fluxes is not reduced.