Abstract: A spindle device of a machine tool, which can prevent the liquefaction of atomized cutting fluid in atomized cutting fluid passage downstream of a straightening unit 14, enhance a responsiveness to an ejecting start or stop instruction, and prevent a waste of cutting fluid. The spindle device for a machine tool has atomized cutting liquid passage (e1, e2) each having a single-shape passage section and formed inside the device ranging from the spindle 1 to the tip end of a cutting tool 13 mounted thereto in one piece, and is operated so as to eject atomized cutting tool 13 via the atomized cutting fluid passages (e1, e2), wherein a straightening unit 14 formed with a plurality of small-diameter passages h are provided in the middle of the cutting liquid passages (e1, e2).