Results of computer simulation of the structure of the electromagnetic field of a microwave discharge in a quartz bulb placed in a cylindrical resonator the plasma of which is confined by a magnetic trap are presented. The cold plasma approximation is used. The cylindrical resonator is excited through a narrow slot in the lateral wall. It is shown that the traditional model of the electron cyclotron resonance in crossed fields in the discharge under study is applicable at low electron densities. An increase in the density is accompanied by the formation of a wave propagating in the azimuthal direction from the excitation region. With a further increase in the electron density, the absorption coefficient of the wave decreases and the angular distribution of the field has the form of a standing wave.