A monomer (1) is prepared by reacting a compound (9) with a base or metal to form a metal enolate reagent, and reacting the metal enolate reagent with an acyloxyketone compound (8). A polymer derived from the monomer is used as base resin to formulate a resist composition, which is shelf stable and displays a high dissolution contrast, controlled acid diffusion and low roughness in forming positive pattern via alkaline development and in forming negative pattern via organic solvent development.