To solve the problem that a photovoltaic power generation device which is a photon power generation device practically used at present does not have performance capable of generating power by absorbing gamma (γ) rays having photon energy 10⁵ times as great as solar photons, such that a material capable of absorbing the gamma rays or a substitutive technology with existing materials should be developed.

When penetrating a material, γ-rays generate scattering γ-rays, heat, and a little electrons (Auger electron) and most of them are continued as transmission γ-rays. A number of photovoltaic power generation devices of a practically used technology are then overlapped to constitute a parallel power collection device. This is irradiated with γ-rays, a little generated electrons are obtained each time γ-rays are transmitted through one panel of the photovoltaic power generation device and simultaneously, γ-rays are attenuated. When attenuated sunlight and energy reach a substantially equal level, power generation efficiency closer to that as a photovoltaic power generation device is obtained. The required number of panels to be overlapped is determined on the condition that transmission γ-rays are not generated from the final panel.