04-03U

We evaluate the thermodynamic functions for an Ising-like magnet near the critical point in the presence of an external field. The calculations are performed on the microscopic level in the three-dimensional space. We described the critical behaviour of the system at $T>T_c$ in the cases of both weak and strong fields. The obtained expressions for the free energy, order parameter, susceptibility, entropy and specific heat are the explicit functions of the temperature, field strength and microscopic parameters of the system.