An apparatus for reducing transmission shock of an automatic transmission may include a piston operated by a control pressure, a clutch performing a clutching operation by an operation of the piston, and a cushion spring arranged between the piston and the clutch which varies by stages in stiffness of the spring with an operating position of the piston. The cushion spring may be formed with one or more sets of a plurality of curved-surface springs bent in an operating direction of the clutch and connected with each other, each set of the plurality of curved-surface springs having a different bending height.