Resist composition and method of forming resist pattern

A resist composition which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid, the resist composition comprising:

• a polymeric compound (A1) comprising a structural unit derived from a compound represented by general formula (a0-1) shown below,
• an acid generator (B1) represented by general formula (b1) shown below, and
• a photodecomposable base (D1) which is decomposed upon exposure and then loses the ability to control acid diffusion:
• wherein Rax0 represents a polymerizable group-containing group;
• Wax0 represents an aromatic hydrocarbon group having a valency of (nax0+1), provided that Rax0 and Wax0 may together form a condensed ring structure;
• nax0 represents an integer of 1 to 3;
• Yax01 represents a carbonyl group or a single bond;
• Rax01 represents a hydrogen atom or a hydrocarbon group which may have a substituent;
• R101 represents a cyclic group which may have a substituent, a chain alkyl group which may have a substituent or a chain alkenyl group which may have a substituent;
• R102 represents a fluorine atom or a fluorinated alkyl group having 1 to 5 carbon atoms;
• Y101 represents a single bond or a divalent group containing an oxygen atom;
• V101 represents an alkylene group, a fluorinated alkylene group or a single bond;
• m represents an integer of 1 or more, and M′m+represents an onium cation having a valency of m.