A photoresist composition comprising an acid generator and a resin which comprises one or more structural units (a1) derived from a monomer (a1) having an acid-liable group, all of monomers (a1) showing a distance of Hansen solubility parameters between the monomer (a1) and butyl acetate in the range of 3 to 5, the distance being calculated from formula (1): R=(4×(δdm−15.8)2+(δpm−3.7)2+(δhm−6.3)2)1/2  (1) in which δdm represents a dispersion parameter of a monomer, δpm represents a polarity parameter of a monomer, δhm represents a hydrogen bonding parameter of a monomer, and R represents a distance of Hansen solubility parameters, and at least one of the monomers (a1) showing a difference of R between the monomer (a1) and a compound in which an acid is removed from the monomer (a1) in the range of not less than 5.