A support shaft of a spindle unit having a through hole in which wires are laid has a structure that can obtain much spatial room so as to prevent a break in cables and to be compatible with a high-output spindle motor. A machine-tool spindle head 1 includes a support head 6 that drives a spindle unit 4 for indexing around a turn axis (A-axis) of the spindle unit 4 by rotatably supporting a pair of support shafts 9 coupled to the spindle unit 4 on the A-axis by a pair of fork arms 7 and bearings 13. The pair of support shafts 9 have through holes 12 in which a plurality of wires 22 extending from the spindle unit 4 are laid, the plurality of wires 22 are divided into two wire groups, and the wire groups are separately laid in the pair of support shafts 9.