It is well known among mushroom farmers that many mushrooms extraordinarily grow within several tens of meters around the spot where lightning strikes. It is supposed that the electrical stimulus of thunderbolts into myceliated logs accelerates the generation or development of mushrooms. Unfortunately, we cannot control natural thunderbolts but we can create artificial thunderbolts such as the pulsed high voltages of pulsed power technology. We started this study in 2002 and reported at PPC 2003 about the effect of an increase in production of shiitake mushrooms. The results showed that the yield from logs to which pulsed high voltage was applied was twice as great as those that received no electrical stimulus. . Although mushrooms have been cultured in the forest using oak logs since old times, automated indoor production is today's standard. The room temperature and humidity in mushroom factories can be suitably controlled. Bottles nested in trays are filled with sawdust and other materials, inoculated with mushroom mycelium, incubated, and finally grown and harvested. In this paper some experiments to increase production of mushrooms from sawdust bottles are described. After the experiments, an electrical stimulator was finally designed and installed at a mushroom factory in February 2005. Pulsed high voltages up to 140kV were applied to sawdust bottles as an electrical stimulus. Application of pulsed high voltages increased the yield of mushrooms by 13 to 15 percent compared with mushrooms to which it was not applied.