A lubricating agent, comprising: an ionic liquid formed from a Bronsted acid and a Bronsted base, (i) wherein the ionic liquid is represented by the following General Formulas, or: wherein R 1, R 2, R 3, and R 4 are independently a hydrogen atom, or a linear hydrocarbon group having 10 or more carbon atoms, wherein at least one of R 1, R 2, R 3, and R 4 is a hydrogen atom, and wherein at least one of R 1, R 2, R 3, and R 4 is a linear hydrocarbon group having 10 or more carbon atoms; wherein R 11 denotes the linear hydrocarbon group having 10 or more carbon atoms and being attached to a carbon atom in a bicyclo ring; wherein R 21 denotes the linear hydrocarbon group having 10 or more carbon atoms and being attached to a carbon atom or a nitrogen atom in a bicyclo ring; wherein the Bronsted acid is perfluoroalkyl sulfonic acid, a compound represented by the following Structural Formula, a compound represented by the following Structural Formula, a compound represented by the following Structural Formula, or a compound represented by the following Structural Formula: or (ii) wherein the ionic liquid is represented by General Formula depicted above, wherein R 1, R 2, R 3, and R 4 are independently a hydrogen atom, or 2-heptylundecyl, wherein one of R 1, R 2, R 3, and R 4 is 2-heptylundecyl, and wherein the Bronsted acid is trifluoromethane sulfonic acid (CF 3 SO 3 H); and wherein a difference between a pKa value of the Bronsted acid in water and a pKa value of the Bronsted base in water is 12 or more. (i) wherein the ionic liquid is represented by the following General Formulas, or: wherein R 1, R 2, R 3, and R 4 are independently a hydrogen atom, or a linear hydrocarbon group having 10 or more carbon atoms, wherein at least one of R 1, R 2, R 3, and R 4 is a hydrogen atom, and wherein at least one of R 1, R 2, R 3, and R 4 is a linear hydrocarbon group having 10 or more carbon atoms; wherein R 11 denotes the linear hydrocarbon group having 10 or more carbon atoms and being attached to a carbon atom in a bicyclo ring; wherein R 21 denotes the linear hydrocarbon group having 10 or more carbon atoms and being attached to a carbon atom or a nitrogen atom in a bicyclo ring; wherein the Bronsted acid is perfluoroalkyl sulfonic acid, a compound represented by the following Structural Formula, a compound represented by the following Structural Formula, a compound represented by the following Structural Formula, or a compound represented by the following Structural Formula: or wherein R 1, R 2, R 3, and R 4 are independently a hydrogen atom, or a linear hydrocarbon group having 10 or more carbon atoms, wherein at least one of R 1, R 2, R 3, and R 4 is a hydrogen atom, and wherein at least one of R 1, R 2, R 3, and R 4 is a linear hydrocarbon group having 10 or more carbon atoms; wherein R 11 denotes the linear hydrocarbon group having 10 or more carbon atoms and being attached to a carbon atom in a bicyclo ring; wherein R 21 denotes the linear hydrocarbon group having 10 or more carbon atoms and being attached to a carbon atom or a nitrogen atom in a bicyclo ring; wherein the Bronsted acid is perfluoroalkyl sulfonic acid, a compound represented by the following Structural Formula, a compound represented by the following Structural Formula, a compound represented by the following Structural Formula, or a compound represented by the following Structural Formula: or (ii) wherein the ionic liquid is represented by General Formula depicted above, wherein R 1, R 2, R 3, and R 4 are independently a hydrogen atom, or 2-heptylundecyl, wherein one of R 1, R 2, R 3, and R 4 is 2-heptylundecyl, and wherein the Bronsted acid is trifluoromethane sulfonic acid (CF 3 SO 3 H);