The present invention relates to a valve structure of a shock absorber, in which a rebound-side stepped portion for supporting a rebound-side disc valve is integrally molded with an upper surface of a piston, and a compression-side inner stepped portion and a compression-side outer stepped portion for supporting a compression-side disc valve are integrally molded with a lower surface of the piston to omit a retainer for supporting a disc valve, thereby simplifying a structure and reducing manufacturing costs and weight of the valve structure, and a side surface of the piston is used to form compression channels, thereby easily securing a space.