We present here the results of gamma-ray emission intensity measurements made during thunderstorm. The gamma-ray intensity background (GRB) grows up in an order of magnitude in the active phase of a storm. This growth is shown to be directly connected with the growth of the thundercloud electric field. Besides, the fast changes of GRB (GRB-jumps) are revealed. GRB-jumps are shown to be determined by atmospheric discharges exactly, what mean the strong direct influence of the electric field in atmosphere on gamma-ray emission.