A washing machine comprising: - an auxiliary receiving platform which is provided on a water-supply flow pathway for the supply of washing water, and which constitutes a container structure able to support a solid additive when such an additive is introduced; and - an additive storage compartment which is formed at a detergent box body and fastened to the underside of the auxiliary receiving platform, and which stores washing water in which the solid additive has been dissolved; - a siphon tube protruded upward from the additive storage compartment - wherein a bottom surface of the auxiliary receiving platform is formed at a position relatively lower than an upper opening end of the siphon tube; - water supply control valves that are mounted on the water-supply flow pathway; and - a controller for controlling the water supply control valves to be operated, characterized in that - the auxiliary receiving platform comprises an opening port which is formed at the base to directly introduce a liquid additive into the additive storage compartment when the liquid additive is introduced, and a support plate which is formed at one side of the opening port to support a solid additive when the solid additive is introduced in order to ensure a sufficient amount of time for the solid additive to be dissolved in the firstly supplied water, - the auxiliary receiving platform has an overflow surface formed at one bottom side thereof, whose bottom is relatively shallower than the position of the support plate, and a plurality of drainage holes are formed on the overflow surface to introduce solid additive into the additive storage compartment, and - the siphon tube is positioned below the overflow surface. - an auxiliary receiving platform which is provided on a water-supply flow pathway for the supply of washing water, and which constitutes a container structure able to support a solid additive when such an additive is introduced; and - an additive storage compartment which is formed at a detergent box body and fastened to the underside of the auxiliary receiving platform, and which stores washing water in which the solid additive has been dissolved; - a siphon tube protruded upward from the additive storage compartment - wherein a bottom surface of the auxiliary receiving platform is formed at a position relatively lower than an upper opening end of the siphon tube; - water supply control valves that are mounted on the water-supply flow pathway; and - a controller for controlling the water supply control valves to be operated, characterized in that - the auxiliary receiving platform comprises an opening port which is formed at the base to directly introduce a liquid additive into the additive storage compartment when the liquid additive is introduced, and a support plate which is formed at one side of the opening port to support a solid additive when the solid additive is introduced in order to ensure a sufficient amount of time for the solid additive to be dissolved in the firstly supplied water, - the auxiliary receiving platform has an overflow surface formed at one bottom side thereof, whose bottom is relatively shallower than the position of the support plate, and a plurality of drainage holes are formed on the overflow surface to introduce solid additive into the additive storage compartment, and - the siphon tube is positioned below the overflow surface.