The present invention includes: a power supply (105) capable of applying a short pulse voltage which retains voltage at the level of 50% or higher of the peak voltage value for 5 microseconds or less; and a switch (108) for switching the power supply connection between a pair of growth promoting electrodes (106) and a pair of disinfectant electrodes (107), wherein roots (101a) of a plant (101) are present between the growth promoting electrodes, and no plant roots are present between the disinfectant electrodes.
