A zoom lens system, comprising, in order from an object side: a first lens unit having a positive refractive power that does not move for magnification-varying; a second lens unit having a negative refractive power that moves for magnification-varying; a third lens unit having one of a positive refractive power and a negative refractive power that moves for magnification-varying; and a fourth lens unit having a positive refractive power that does not move for magnification-varying, wherein: when an Abbe constant of a positive lens Lp having a smallest Abbe constant among lenses constituting the first lens unit is denoted by vp, a partial dispersion ratio thereof is denoted by θp, a refractive power thereof is denoted by φp, an average value of Abbe constants of positive lenses of the first lens unit except the positive lens Lp is denoted by vap, an average value of partial dispersion ratios of negative lenses of the first lens unit is denoted by θan, a refractive power of the first lens unit is denoted by φ1, a refractive power of an entire zoom lens system at a telephoto end is denoted by φtele, an average value of Abbe constants of the negative lenses among the lenses constituting the first lens unit is denoted by van, and a sum of refractive powers of the negative lenses is denoted by φn, the following expressions are satisfied: − 0.03 < θ p − θ an / θ ⁢ an < 0.15; 0.005 < 1 / vp − 1 / vap / φ 1 / φ tele < 0.030; 0.05 < φ ⁢ p / φ 1 < 0.4; 0.05 < 1 / van − 1 / vap / φ p / φ 1 < 0.5; and − 1.0 < φ ⁢ n / φ 1 < − 0.4, provided that, when a refractive index for g-line is denoted by Ng, a refractive index for C-line is denoted by NC, a refractive index for d-line is denoted by Nd, and a refractive index for F-line is denoted by NF, the following expressions are satisfied. Abbe constant v = Nd − 1 / NF − NC Partial dispersion ratio θ = Ng − NF / NF − NC a first lens unit having a positive refractive power that does not move for magnification-varying; a second lens unit having a negative refractive power that moves for magnification-varying; a third lens unit having one of a positive refractive power and a negative refractive power that moves for magnification-varying; and a fourth lens unit having a positive refractive power that does not move for magnification-varying, wherein: when an Abbe constant of a positive lens Lp having a smallest Abbe constant among lenses constituting the first lens unit is denoted by vp, a partial dispersion ratio thereof is denoted by θp, a refractive power thereof is denoted by φp, an average value of Abbe constants of positive lenses of the first lens unit except the positive lens Lp is denoted by vap, an average value of partial dispersion ratios of negative lenses of the first lens unit is denoted by θan, a refractive power of the first lens unit is denoted by φ1, a refractive power of an entire zoom lens system at a telephoto end is denoted by φtele, an average value of Abbe constants of the negative lenses among the lenses constituting the first lens unit is denoted by van, and a sum of refractive powers of the negative lenses is denoted by φn, the following expressions are satisfied: − 0.03 < θ p − θ an / θ ⁢ an < 0.15; 0.005 < 1 / vp − 1 / vap / φ 1 / φ tele < 0.030; 0.05 < φ ⁢ p / φ 1 < 0.4; 0.05 < 1 / van − 1 / vap / φ p / φ 1 < 0.5; and − 1.0 < φ ⁢ n / φ 1 < − 0.4, provided that, when a refractive index for g-line is denoted by Ng, a refractive index for C-line is denoted by NC, a refractive index for d-line is denoted by Nd, and a refractive index for F-line is denoted by NF, the following expressions are satisfied. Abbe constant v = Nd − 1 / NF − NC Partial dispersion ratio θ = Ng − NF / NF − NC