An apparatus for treating laundry, the apparatus comprising: a cabinet having an entrance and a door for opening and closing the entrance; a tub providing a space for storing water therein and having a tub entrance provided to a surface facing a direction having the entrance located therein; a drum rotatably provided within the tub to provide a space for storing the laundry therein and having a drum entrance provided to the surface facing the direction having the entrance located therein; an insulating part having a first fixing body in a cylindrical shape fixed to the entrance, a second fixing body in a cylindrical shape fixed to the tub entrance, a connecting body connecting the first and second fixing bodies (411, 412) together to form a space for storing liquid therein between the first fixing body and the second fixing body, and an inflow pipe perforating the first fixing body; a storage part provided within the cabinet to provide a space for storing detergent therein; a discharge pipe configured to guide the detergent in the storage part to the inflow pipe, the discharge pipe comprising: a storage part connecting pipe configured to discharge the detergent of the storage part; an insulating part connecting pipe connected to the inflow pipe; a trap forming pipe configured to connect the storage part connecting pipe and the insulating part connecting pipe to form one of a P-trap, a U-trap and an S-trap between the storage part connecting pipe and the insulating part connecting pipe; and a decelerating part (91, 92, 93) configured to decelerate a flow speed of water moving from the trap forming pipe to the insulating part connecting pipe, characterized in that: the decelerating part is located inside the insulating part connecting pipe. a cabinet having an entrance and a door for opening and closing the entrance; a tub providing a space for storing water therein and having a tub entrance provided to a surface facing a direction having the entrance located therein; a drum rotatably provided within the tub to provide a space for storing the laundry therein and having a drum entrance provided to the surface facing the direction having the entrance located therein; an insulating part having a first fixing body in a cylindrical shape fixed to the entrance, a second fixing body in a cylindrical shape fixed to the tub entrance, a connecting body connecting the first and second fixing bodies (411, 412) together to form a space for storing liquid therein between the first fixing body and the second fixing body, and an inflow pipe perforating the first fixing body; a storage part provided within the cabinet to provide a space for storing detergent therein; a discharge pipe configured to guide the detergent in the storage part to the inflow pipe, the discharge pipe comprising: a storage part connecting pipe configured to discharge the detergent of the storage part; an insulating part connecting pipe connected to the inflow pipe; a trap forming pipe configured to connect the storage part connecting pipe and the insulating part connecting pipe to form one of a P-trap, a U-trap and an S-trap between the storage part connecting pipe and the insulating part connecting pipe; and a decelerating part (91, 92, 93) configured to decelerate a flow speed of water moving from the trap forming pipe to the insulating part connecting pipe, characterized in that: a storage part connecting pipe configured to discharge the detergent of the storage part; an insulating part connecting pipe connected to the inflow pipe; a trap forming pipe configured to connect the storage part connecting pipe and the insulating part connecting pipe to form one of a P-trap, a U-trap and an S-trap between the storage part connecting pipe and the insulating part connecting pipe; and a decelerating part (91, 92, 93) configured to decelerate a flow speed of water moving from the trap forming pipe to the insulating part connecting pipe, characterized in that: the decelerating part is located inside the insulating part connecting pipe.