To ensure that an electric power cable and a signal cable are laid easily over short distances while suppressing an effect of electromagnetic wave noise on the signal cable, an electric power cable is laid along a route that passes through only a right outside space in a lower position than an upper end of a right vertical plate, while a signal cable is laid along a bypass route that extends from a generator motor in a lower position than the upper end of the right vertical plate, passes through a rear portion cable insertion hole into an intermediate space between the right vertical plate and a left vertical plate, and returns to the right outside space from the intermediate space through a front portion cable insertion hole.