A machining center is provided with a guard that covers a processing portion of a machine tool. An openable and closable operation door is provided at the guard front. The operation door is arched along a vertical direction from the guard surface. The operation door is provided with a handle used to open and close the operation door. The operation door is curved on an arched line that reaches a highest point at its center and lowers toward the top and bottom ends. The guard is provided with half-round LED display means protruding from the guard surface. The operation door is made of carbon fiber.