A pattern can be precisely formed by irradiating, with an active energy beam, a positive sensitive resin composition according to this invention comprising a base polymer, an ether-bond-containing olefinic unsaturated compound and an acid-generating agent, where the base polymer is a copolymer comprising the structural units represented by formulas (1) to (3): ##STR1## where R¹ and R³ are each independently hydrogen or methyl and R² is C₁-C₆ straight or branched unsubstituted alkyl or C₁-C₆ straight or branched substituted alkyl, wherein a, b and c are 0.05 to 0.7, 0.15 to 0.8 and 0.01 to 0.5, respectively and a+b+c=1.