A 2-phenylmorpholin-5-one derivative having the formula (I): wherein R1 represents a C1 to C8 alkyl group, a C3 to C7 cycloalkyl group or an indanyl group, R2 represents a C1 to C4 alkyl group, R3 represents a hydrogen atom, a C1 to C5 alkyl group, etc., R4 represents a hydrogen atom, a C1 to C6 alkyl group, etc., R5, R6 represent a hydrogen atom, a C1 to C5 alkyl group, etc., an optical isomer thereof or a pharmacologically acceptable salt thereof, or a hydrate or solvate thereof and a pharmaceutical composition containing the same. The above compound has a strong type IV phosphodiesterase (PDE) inhibitory activity and has bronchodilater and antiinflammatory effects.