Positive resist composition and pattern forming method using the same

A positive resist composition comprising:

• (A) a compound capable of generating an acid upon irradiation with actinic rays or radiation;
• and (B) a resin of which solubility in an alkali developer increases under the action of an acid, the resin comprising at least a repeating unit represented by the following formula (B1) or (B2):
• wherein
• Z represents an alkyl group, a hydroxyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, an acyl group, an acyloxy group, a cycloalkyl group, an aryl group, a carboxyl group, an alkyloxycarbonyl group, an alkylcarbonyloxy group or an aralkyl group,
• Lc1 represents an atomic group for forming a lactone structure together with two carbon atoms of the aromatic ring,
• Lc2 represents a group having a lactone structure,
• Ra and Rb each independently represents a hydrogen atom, an alkyl group, a hydroxyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, an acyl group, an acyloxy group, a cycloalkyl group, an aryl group, a carboxyl group, an alkyloxycarbonyl group, an alkylcarbonyloxy group or an aralkyl group,
• m represents an integer of 1 to 4, and
• n represents an integer of 0 to 4.