In this paper, the \lambda\phi^4 scalar feld effective action, in the
one-loop approximation, is calculated by using the Krein space quantization. We
show that the effective action is naturally fnite and the singularity does not
appear in the theory. The physical interaction mass, the running coupling
constant and \beta-function are then calculated. The effective potential which
is calculated in the Krein space quantization is different from the usual
Hilbert space calculation, however we show that \beta-function is the same in
the two different methods.Comment: 11 page