A lubricant including: an ionic liquid, which includes a conjugate acid (B+) and a conjugate base (X−), and is protic, wherein the ionic liquid is represented by the following general formula (1), and wherein the conjugate base is a conjugate base of sulfonic acid, a conjugate base of sulfonimide, or a conjugate base of trisulfonylmethide: where R1 and R2 each represent a hydrogen atom or R1 and R2 form a benzene ring together with carbon atoms to which R1 and R2 are bonded, R3 represents a to straight-chain hydrocarbon group having 10 or more carbon atoms, and R4 represents a hydrogen atom or a hydrocarbon group in the general formula (1).