Examples of the alkoxy group include alkoxy groups including 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, a propoxy group and a butoxy group. [0079] Examples of monomers corresponding to repeating units represented by formulae (Ia) and (Ib) respectively are illustrated below: [0080] The present acid-decomposable resin (A) may further contain repeating units having partial structur