Resist composition and method for forming resist pattern

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

• a base material component (A) whose solubility in the developing solution changes under the action of the acid and which contains a polymer compound (A1) having a structural unit (a0) represented by the following general formula (a0-1);
• and
• an acid diffusion control agent component (D) which contains a compound (D1) whose a conjugate acid has an acid dissociation constant (pKa) of less than 3:
• wherein R is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a halogenated alkyl group having 1 to 5 carbon atoms;
• Va0 is a divalent hydrocarbon group which may have a substituent;
• na0 is an integer of 0 to 2;
• Ra1 and Ra2 each independently represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group, or an alkylthio group, or Ra1 and Ra2 may be bonded to each other so as to form an alkylene group having 1 to 6 carbon atoms, which may contain an oxygen atom or a sulfur atom, an ether bond, or a thioether bond;
• Ra′01 is a halogen atom, an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, a hydroxyalkyl group having 1 to 6 carbon atoms, of which the hydroxy group may be protected by a protective group and which may have a halogen atom, a carboxy group which may forma salt, or a substituted oxycarbonyl group;
• p0 is an integer of 0 to 8, and in a case where two or more Ra′01's are present, the plural Ra′01's may be the same as or different from each other;
• X is a group represented by general formula (a0-r-1), a cyano group, a halogen atom, a halogenated alkyl group, —C(═O)ORa5, —OC(═O)Ra5, —CON (Ra6)(Ra7), —SO2N(Ra8)(Ra9), or —SO2Ra0, in which Ra5 to Ra9 each independently represent a hydrogen atom or an alkyl group, Ra0 is an alkyl group, and in the formula (a0-r-1), Ra3 and Ra4 each independently represent a hydrogen atom or a nonaromatic hydrocarbon group which may have a substituent, or Ra3 and Ra4 may be bonded to each other so as to form a ring with the carbon atom to which Ra3 is bonded and the nitrogen atom to which Ra4 is bonded, and a symbol of * represents a bond;
• and
• q0 is an integer of 1 to 9, and in a case where two or more X's are present, the plural X's may be the same as or different from each other.