For quarantine treatment of a farming and forestry product for pest control, a method and a device may irradiate logs as a phytosanitary treatment with electron beams. The method may include: spreading the logs; aligning the spread logs to be flush at one end; conveying the spread and flush logs laterally; conveying the logs longitudinally through an irradiation field formed by accelerators to provide treatment of irradiation with the electron beams; throwing the irradiated logs out; and laterally conveying the logs away. The device may include a conveying device for conveying the logs, a shielding structure surrounding the conveying device, and accelerators provided in the conveying path of the conveying device. Two or more accelerators may be provided in centrosymmetry about the conveying path.