A mortise/tenon machine has a base which includes two side plates, a guiding plate installed between the side plates transversely and horizontally, numbers of openings formed on a side of the guiding plate, and a rail member installed between the side plates and in the same horizontal position of the guiding plate. A workpiece is slideably disposed on the openings. A sliding base is slideably mounted on the rail member. A working platform includes a bit installed at a first end thereof, with the bit extending from a desired opening, and with another end of the working platform longitudinally disposed on the sliding base.