The existence and uniqueness of solutions and asymptotic estimate of solution formulas are studied for the following initial value problem: g t y t ay t 1 f t, y t , t 0 K t, s, y t , y s ds , y 0 0, t ∈ 0, t 0 , where a > 0 is a constant and t 0 > 0. An approach which combines topological method of T. Ważewski and Schauder's fixed point theorem is used.