The quantum field theory is presented in terms of Euclidean parameters. It is shown that this theory is equivalent to the conventional one in terms of the Minkowski parameters, if we confine ourselves to the case of local fields, and it is suggested that the former is more adequate to describe an internal structure of an elementary particle than the latter. There is no necessity that the parameter space of field theory is Minkowski, because it has no direct connection with the macroscopic space. It is enough that expectation values of observable quantities are covariant under Lorentz transformations. The theory shown in this paper satisfies this requirement.