The present invention relates to a positive-working photosensitive resin precursor composition which is characterized in that it contains (a) polymer in which the chief component comprises structural units of the kind where the bonding between structural units is represented by general formula (1) and (b) photoacid generator, and it can form a pattern by light irradiation and subsequent developing, and the total carboxyl groups contained in said polymer is from 0.02 to 2.0 mmol/g, and it provides a photosensitive resin composition of high sensitivity which can be developed by alkali. (R1 is an organic group of valency from 3 to 8 having at least 2 carbon atoms, R2 is an organic group of valency from 2 to 6 having at least 2 carbon atoms, R3 is hydrogen or an organic group with from 1 to 10 carbons. n is an integer of value from 3 to 100,000, m is 1 or 2, p and q are integers of value from 0 to 4 and p+q>0).