A main mouth of a brick molding machine is disclosed. In a main mouth installed between a pressing unit of a brick molding machine and a mold in an assembled structure, the main mouth of a brick molding machine comprises a bolt insertion hole that passes through two opposing sides among upper and lower sides and left and right sides between inlet and outlet parts of a mouth body; a resistance member that includes an attaching surface attached to an inner surface of the mouth body having the bolt insertion hole therein, and a resistance surface protruded in a direction of an inner surface of the mouth body; a nut member embedded in the attaching surface of the resistance member with a part of the same being exposed; and an engaging bolt that is inserted from an outer side of the mouth body through the bolt insertion hole and thread-engaged with the nut member embedded in the resistance member for thereby fixing the resistance member to an inner surface of the mouth body.