Abstract: An air jet for a machine tool to clean cutting dust has a housing with a hole and an outlet. An eccentric member has a cam and is provided in the housing which the eccentric member is driven by a power resource of the machine tool for rotation. An annular transmission is engaged with the eccentric member. A driving member is driven by the transmission for linear reciprocating motion. A flexible film is provided in the housing covering the outlet and has an inlet corresponding to the driving member, wherein the inlet of the film is sealed and the film is pressed for strain while the driving member is moved toward the film, and a tube has an end thereof connected with the outlet.