To provide a lubricating oil that keeps high lubrication performance in a broad temperature range and has little volume change by temperature.

The lubricating oil consists of an ionic liquid that is a salt of an amidinium cation such as 1,3-dimethyl imidazolium, 1,3-diethyl imidazolium, 1-ethyl-3-methyl imidazolium and 1,2,3-trimethyl imidazolium with an anion expressed by formula (2). In formula (2), each of R3 and R4 independently represents F or CnF2n+1, wherein n is an integer of 1 to 4.