There are provided a compound represented by a general formula (b1-1) shown below suitable as an acid generator for a resist composition, a compound represented by a general formula (I) shown below suitable as a precursor for the compound represented by the general formula (b1-1), an acid generator, a resist composition, and a method of forming a resist pattern.[Chemical Formula 1] X—Q1—Y1—SO3−M+  (I) X—Q1—Y1—SO3−A+  (b1-1) (wherein, Q1 represents a bivalent linking group or a single bond; Y1 represents an alkylene group which may contain a substituent group or a fluorinated alkylene group which may contain a substituent group; X represents an aromatic cyclic group of 5 to 30 carbon atoms which contains a fluorine atom and may contain a substituent group; M+ represents an alkali metal ion; and A+ represents an organic cation.).