This reduction processing apparatus for a steel-making slag that continuously performs reduction processing to a hot steel-making slag by using an electric furnace includes: a slag-supplying container that charges the hot steel-making slag into the electric furnace; an electrode that is provided at the electric furnace and heats a molten slag layer on a molten iron produced by reducing the hot steel-making slag; an auxiliary-raw-material supplying unit that supplies an auxiliary-raw-material including a reducing agent to the molten slag layer; and a tilting unit that tilts the slag-supplying container and adjusts a charging amount of the hot steel-making slag to the electric furnace.