A method for supplying cutting oil which adopts the following processes in a machine tool for cutting plural kinds of work pieces: a: setting cutting times t 1,...,t i,...,t n for work pieces 1,...,i,...,n and selection of cutting oil to be used wherein n is an integer of not less than one, and i denotes a kind of work of i th order, b: setting quantities q 1,...,q i,...,q n of the cutting oil supplied per unit time according to a cutting area of the work pieces 1,...,i,...,n, where the cutting oil selected by process a is used, c: setting a quantity q'" of a fixed value supplied per unit time under conditions that selecting a maximum value q m among q 1,...,q i,...,q n, an inequality of q′′′>q m is satisfied, and supplying the cutting oil to the cutting-oil tank by the quantity q'" continuously corresponding to cutting a part of work pieces 1,...,i, then stopping supply of the cutting oil to the tank in a stage that the cutting-oil tank is filled with the cutting oil corresponding to cutting the work piece i+1, and supplying again the cutting oil to the cutting-oil tank by the quantity q'" at a stage that the quantity of the cutting oil retained in the cutting-oil tank has reached a minimum reference quantity due to the thus stopped supply, wherein the stopping and the supplying are repeated according to necessary case, d: supplying the cutting oil to the cutting area with setting quantities of the cutting oil to be q 1 t 1,...,q i t i,...,q n t n on cutting the work pieces 1,...,i,...,n by flowing out from the cutting-oil tank. a: setting cutting times t 1,...,t i,...,t n for work pieces 1,...,i,...,n and selection of cutting oil to be used wherein n is an integer of not less than one, and i denotes a kind of work of i th order, b: setting quantities q 1,...,q i,...,q n of the cutting oil supplied per unit time according to a cutting area of the work pieces 1,...,i,...,n, where the cutting oil selected by process a is used, c: setting a quantity q'" of a fixed value supplied per unit time under conditions that selecting a maximum value q m among q 1,...,q i,...,q n, an inequality of q′′′>q m is satisfied, and supplying the cutting oil to the cutting-oil tank by the quantity q'" continuously corresponding to cutting a part of work pieces 1,...,i, then stopping supply of the cutting oil to the tank in a stage that the cutting-oil tank is filled with the cutting oil corresponding to cutting the work piece i+1, and supplying again the cutting oil to the cutting-oil tank by the quantity q'" at a stage that the quantity of the cutting oil retained in the cutting-oil tank has reached a minimum reference quantity due to the thus stopped supply, wherein the stopping and the supplying are repeated according to necessary case, selecting a maximum value q m among q 1,...,q i,...,q n, an inequality of q′′′>q m is satisfied, and supplying the cutting oil to the cutting-oil tank by the quantity q'" continuously corresponding to cutting a part of work pieces 1,...,i, then stopping supply of the cutting oil to the tank in a stage that the cutting-oil tank is filled with the cutting oil corresponding to cutting the work piece i+1, and supplying again the cutting oil to the cutting-oil tank by the quantity q'" at a stage that the quantity of the cutting oil retained in the cutting-oil tank has reached a minimum reference quantity due to the thus stopped supply, wherein the stopping and the supplying are repeated according to necessary case, d: supplying the cutting oil to the cutting area with setting quantities of the cutting oil to be q 1 t 1,...,q i t i,...,q n t n on cutting the work pieces 1,...,i,...,n by flowing out from the cutting-oil tank.