Abstract: A method of preageing vacuum devices comprises discharging, through the gap between the electrodes (14, 15) of a vacuum device (16) upon breakdown of said gap, an open long-line length (4) precharged to a voltage lower than the breakdown voltage and disconnected after breakdown in a time interval determined by the parameters of the long-time length (4).An apparatus for preageing vacuum devices comprises terminals (1, 2) to connect a vacuum device (16) thereto, a breakdown voltage power supply (3) connected to the terminals (1, 2) also connected to which, through a diode (8), is an open long-line length (4) coupled with a charge voltage power supply (5). The long-line length (4) is discharged through the interelectrode gap of a vacuum device (16), upon breakdown of the gap, during a time interval equal to twice the time of propagation of an electromagnetic wave along the long-line length (4), after which the voltage across the latter changes its sign, causing a cuttoff state of the diode (8).