Abstract: A machining center comprises a bed and an arch-shaped column having a pair of post portions spaced from each other in the transverse direction of the bed and a crossbeam portion connecting the post portions. A spindle head is supported on the crossbeam portion of the column to be movable both in the vertical direction and in the transverse direction of the bed and supports a spindle which is rotatable about a substantially vertical rotating shaft and on which a tool is demountably mounted. A base table is supported on the bed between the post portions of the column to be movable back and forth and a support supported on the base table by a supporting portion of the base table to be rotatable in an indexing manner about a rotating shaft inclined upward toward the front end thereof at 45.degree. to the rotating shaft of the spindle. A turn table is provided on the support to be rotatable in an indexing manner about a rotating shaft at 45.degree.