An additive for water-based paint, comprising a siloxane-branched polyether-modified silicone shown by an average composition formula R 1 a R 2 b R 3 c SiO (4-a-b-c)/2 and having a weight-average molecular weight in a range of 500 to 100,000, wherein in the formula each R 1 is identical to or different from one another and represents an organic group selected from an alkyl group, an aryl group, and an aralkyl group having 1 to 30 carbon atoms, and an organic group shown by a general formula -C m H 2m -O-(C 2 H 4 O) d (C 3 H 6 O) e R 4; each R 2 represents a group shown by a general formula -C m H 2m -O-(C 2 H 4 O) f (C 3 H 6 O) g -R 5; each R 3 represents an organosiloxane shown by the following general formula R 4 represents a hydrocarbon group having 4 to 30 carbon atoms, or an organic group shown by R 6 - -; R 5 represents a hydrogen atom, a hydrocarbon group having 1 to 30 carbon atoms, or an organic group shown by R 6 - -; R 6 represents a hydrocarbon group having 1 to 30 carbon atoms; R 1 in the general formula is the same as R 1 in the formula; "a", "b", and "c" respectively satisfy 1.0≤a≤2.5, 0.001≤b≤1.5, and 0.001≤c≤1.5; "d" and "e" respectively represent integers satisfying 0≤d≤50 and 0≤e≤50; "f" and "g" respectively represent integers satisfying 2≤f≤200, 0≤g≤200, and f+g being 3 to 200; "m" represents an integer satisfying 0≤m≤10; "h" represents an integer satisfying 0≤h≤500; and "n" represents an integer satisfying 1≤n≤5, and wherein the siloxane-branched polyether-modified silicone satisfies the following expression and the following expression, 5 ≤ {(a total molecular weight of a (C 2 H 4 O) d part in the general formula and a (C 2 H 4 O) f part in the general formula incorporated in the siloxane-branched polyether-modified silicone)/(a molecular weight of the siloxane-branched polyether-modified silicone)}×20 ≤ 10, and {(a total molecular weight of a (C 3 H 6 O) e part in the general formula and a (C 3 H 6 O) g part in the general formula incorporated in the siloxane-branched polyether-modified silicone)/(a total molecular weight of a (C 2 H 4 O) d part in the general formula and a (C 2 H 4 O) f part in the general formula incorporated in the siloxane-branched polyether-modified silicone)} ≤ 1.0. each R 2 represents a group shown by a general formula -C m H 2m -O-(C 2 H 4 O) f (C 3 H 6 O) g -R 5; each R 3 represents an organosiloxane shown by the following general formula R 4 represents a hydrocarbon group having 4 to 30 carbon atoms, or an organic group shown by R 6 - -; R 5 represents a hydrogen atom, a hydrocarbon group having 1 to 30 carbon atoms, or an organic group shown by R 6 - -; R 6 represents a hydrocarbon group having 1 to 30 carbon atoms; R 1 in the general formula is the same as R 1 in the formula; "a", "b", and "c" respectively satisfy 1.0≤a≤2.5, 0.001≤b≤1.5, and 0.001≤c≤1.5; "d" and "e" respectively represent integers satisfying 0≤d≤50 and 0≤e≤50; "f" and "g" respectively represent integers satisfying 2≤f≤200, 0≤g≤200, and f+g being 3 to 200; "m" represents an integer satisfying 0≤m≤10; "h" represents an integer satisfying 0≤h≤500; and "n" represents an integer satisfying 1≤n≤5, and wherein the siloxane-branched polyether-modified silicone satisfies the following expression and the following expression, 5 ≤ {(a total molecular weight of a (C 2 H 4 O) d part in the general formula and a (C 2 H 4 O) f part in the general formula incorporated in the siloxane-branched polyether-modified silicone)/(a molecular weight of the siloxane-branched polyether-modified silicone)}×20 ≤ 10, and {(a total molecular weight of a (C 3 H 6 O) e part in the general formula and a (C 3 H 6 O) g part in the general formula incorporated in the siloxane-branched polyether-modified silicone)/(a total molecular weight of a (C 2 H 4 O) d part in the general formula and a (C 2 H 4 O) f part in the general formula incorporated in the siloxane-branched polyether-modified silicone)} ≤ 1.0.