Nozzle for machining and optical machining device

In order to switch between emitting and stopping a powder flow while maintaining a steady flow and without stopping the steady flow once started, this nozzle for machining comprises: a supply source for fluid including a powder; a first flowpath through which passes the fluid supplied from the supply source; a second flowpath that supplies the fluid to a nozzle emission port; a third flowpath that releases the fluid outside the nozzle; and a switching means that, when the fluid is to be supplied to the emission port, connects the first flowpath and the second flowpath and, when the fluid is not to be supplied to the emission port, connects the first flowpath and the third flowpath.