Simple field-theoretical approach to critical phenomena is described. In contrast to the Wilson's theory, a description in real 3-dimensions space is used. At the same time the described approach is not the same as Parisi's. Used subtraction scheme is different from the one used by Parisi, but the main point is that we treat changes of
T−TC as explicit perturbations. By such an approach not only the critical domain but also the crossover from critical domain to domain of Landau theory can be described very simply. Consideration is restricted to scalar
ϕ4 model in one-loop approximation.