An electricity supply tool holder for a machining center is provided, and has: a holder body, a stationary coil portion, a rotating coil portion, a lateral fixing portion, and an electrical machinery. The stationary coil portion is provided with a primary coil therein; the rotating coil portion is correspondingly provided with a secondary coil therein; and the lateral fixing portion is fixed on a side of the stationary coil portion used for removably combining with a machining center. When the tool holder is rotated, an external electric power/signal can be transmitted through the lateral fixing portion to the primary coil, then inducing the secondary coil, then the electric power/signal is transmitted to the electrical machinery. Additionally, the lateral fixing portion can be switched into a locked position to temporarily limit rotation, so that it can be used in a machining center of an Automatic Tool Changing (ATC) system.