The present invention relates to an oil agent for carbon-fiber precursor acrylic fiber, including at least one type of compound selected from groups of a hydroxybenzoate (Compound A), a cyclohexanedicarboxylic acid (Compound B and C), a cyclohexanedimethanol and/or a cyclohexanediol and a fatty acid (Compound D and E) and an isophoronediisocyanate-aliphatic alcohol adduct (Compound F), an oil composition for carbon-fiber precursor acrylic fiber, a processed-oil solution for carbon-fiber precursor acrylic fiber, and a method for producing a carbon-fiber precursor acrylic fiber bundle, and a carbon-fiber bundle using the carbon-fiber precursor acrylic fiber bundle.