A method of supplying lubricating oil in cold-rolling by emulsion lubrication, characterized by comprising: using a constant (supply efficiency) obtained under conditions of a specific rolling rate, emulsion supply, emulsion concentration, emulsion temperature, plateout length, rolled material width or roll barrel length, rolling load, grade of the rolled material, and type of lubricating oil and oil film thickness at the time of neat lubrication realized under the specific rolling lubrication conditions to estimate the oil film thickness realized by emulsion lubrication under the specific rolling lubrication conditions and controlling at least one of the emulsion supply, emulsion concentration, emulsion temperature, and plateout length so that the estimated oil film thickness matches with the target oil film thickness.