A large-quadrupedal-animal costume suit modeled after a large quadrupedal animal, the costume suit having a head and mouth part, a neck part, a body part, a foreleg part, a hind leg part, and a tail part and being configured, as a whole, a skeletal member and a skin member covering the skeletal member, wherein the body part, the foreleg part, and the hind leg part communicate with each other to form a single hollow, the hollow has a size allowing a foreleg operator fitting in the foreleg part and a hind leg operator fitting in the hind leg part to fit in as standing upright. Frame-pack support members for the foreleg operator and the hind leg operator are installed in the hollow as being fixed to the skeletal member at the body part, and a frame pack for the foreleg operator and a frame pack for the hind leg operator are provided to the frame-pack support members so as to face each other. The large-quadrupedal-animal costume suit capable of making a realistic movement is provided.