An equalizer device (10, 80) for a parking brake, in which paired engagement portions, with which paired output members (24a, 24b) coupled to brake devices (25a, 25b) of right and left wheels are respectively engaged, are formed so as to be symmetric with respect to an input portion, and which actuates the brake devices (25a, 25b) by pulling the paired output members (24a, 24b) in a state where the equalizer device (10, 80) is oscillable using the input portion as an axis of oscillation when a pulling force for actuating the parking brake is applied to the input portion, the equalizer device (10, 80) comprising: an equalizer body (12, 82) that is formed by connecting paired side plates (18, 20), which extend parallel to each other from a back plate so as to form a U-shape; and a synthetic resin member that is fixedly arranged inside the equalizer body, wherein the equalizer body has paired engagement holes (28a, 28b) that are formed in the back plate, and that allow coupling members (26a, 26b) that couple the output members (24a, 24b) to the brake devices (25a, 25b) to extend outside the equalizer body (12, 82) and prevent the output members (24a, 24b) from passing through the engagement holes (28a, 28b), paired insertion holes (30a, 30b) which are formed in a first side plate, which is one of the paired side plates (18, 20), so as to correspond to the paired engagement holes (28a, 28b), and through which the paired output members (24a, 24b) are inserted to an inner side of the U-shape, and paired slits (32a, 32b) which are formed so as to lie astride the first side plate and the back plate and so as to connect each of the insertion holes (30a, 30b) to each of the engagement holes (28a, 28b) respectively, and into which the coupling members (26a, 26b) are inserted, portions of the back plate, at which the engagement holes (28a, 28b) are formed, serve as the engagement portions, the synthetic resin member has a substantially flat plate shape that is arranged so as to face a portion of an inner face of the first side plate, the portion being a part of the U-shape, and so as to extend parallel to the first side plate, the synthetic resin member includes paired gate portions (58, 60) that are formed so as to partially block the respective paired insertion holes (30a, 30b), that are elastically deformable to allow insertion of the output members (24a, 24b) into the equalizer body (12, 82), and that return to their original form to prevent the output members (24a, 24b) from coming out of the equalizer body (12, 82) through the insertion holes (30a, 30b), characterized by an engagement lug (62, 64) that extends on an outer side of an outer edge of the first side plate and extends beyond an outer face of the first side plate, which is on an opposite side from the inner face, and is engaged with the outer face, and the synthetic resin member is fitted to the equalizer body (12, 82) by the engagement lug (62, 64). an equalizer body (12, 82) that is formed by connecting paired side plates (18, 20), which extend parallel to each other from a back plate so as to form a U-shape; and a synthetic resin member that is fixedly arranged inside the equalizer body, wherein the equalizer body has paired engagement holes (28a, 28b) that are formed in the back plate, and that allow coupling members (26a, 26b) that couple the output members (24a, 24b) to the brake devices (25a, 25b) to extend outside the equalizer body (12, 82) and prevent the output members (24a, 24b) from passing through the engagement holes (28a, 28b), paired insertion holes (30a, 30b) which are formed in a first side plate, which is one of the paired side plates (18, 20), so as to correspond to the paired engagement holes (28a, 28b), and through which the paired output members (24a, 24b) are inserted to an inner side of the U-shape, and paired slits (32a, 32b) which are formed so as to lie astride the first side plate and the back plate and so as to connect each of the insertion holes (30a, 30b) to each of the engagement holes (28a, 28b) respectively, and into which the coupling members (26a, 26b) are inserted, portions of the back plate, at which the engagement holes (28a, 28b) are formed, serve as the engagement portions, the synthetic resin member has a substantially flat plate shape that is arranged so as to face a portion of an inner face of the first side plate, the portion being a part of the U-shape, and so as to extend parallel to the first side plate, the synthetic resin member includes paired gate portions (58, 60) that are formed so as to partially block the respective paired insertion holes (30a, 30b), that are elastically deformable to allow insertion of the output members (24a, 24b) into the equalizer body (12, 82), and that return to their original form to prevent the output members (24a, 24b) from coming out of the equalizer body (12, 82) through the insertion holes (30a, 30b), characterized by an engagement lug (62, 64) that extends on an outer side of an outer edge of the first side plate and extends beyond an outer face of the first side plate, which is on an opposite side from the inner face, and is engaged with the outer face, and the synthetic resin member is fitted to the equalizer body (12, 82) by the engagement lug (62, 64).