To provide a working fluid supplying device employing a simple structure requiring no maintenance of a hose in a recovery circuit for decreasing inner pressure in a working fluid supply passage and recovering working fluid remaining in the working fluid supply passage.

This working fluid supplying device includes a working fluid supplying circuit 5 for supplying working fluid from a working fluid source 0 to the tip through a check valve 1, a rotary joint 2, and the inside of a spindle 3, and a bypass circuit 6 for returning the working fluid in the check valve 1 to the spindle 3 to the working fluid source 0 via a direction control valve 23, in a machine tool comprising a first saddle 13 liftably held by a column 11 provided on the upper surface of a base 9 and a second saddle 15, which is constructed integrally with a main spindle body 16 for rotatably holding the spindle 3, held by the first saddle 13 horizontally movably. The bypass circuit 6 is structured by accessibly loosely inserting a horizontally moving drain pipe 26 mounted to the second saddle 15 into a fixed drain pipe 25 mounted to the first saddle 13.