To provide a cutting fluid which, without using a surfactant and an emulsifier that are harmful to a human body and the environment, has an oil dispersed or emulsified in water; and to provide a cutting fluid supply apparatus which produces the cutting fluid, can suppress its decay without use of a bactericide and permits circulating/reusing the cutting fluid over a long period of time.

The apparatus is equipped with a cutting fluid producing means 3 which produces, without using the surfactant or emulsifier but using an ultrasound oscillator 15, the cutting fluid 2 having the oil dispersed or emulsified in water; a storing means 4 which stores the fluid 2 produced by the means 3; a supplying means which supplies the fluid 2 stored in the means 4 to a cutting portion of a machine tool 5; and a cutting fluid returning means 7 which returns the fluid 2 supplied by the supplying means to the cutting portion of the machine tool 5, to the means 4.