To fabricate artificial crystals with any structure from monosized spherical particles, we have so far manufactured a three-dimensionally particle assembling system with a combination of pick-and-place robotic manipulation and inter-particle laser welding. In the present study, we aimed to assemble large-scale artificial crystals of polyethylene (PE) particles by mean of the new system. In this method, an optimization of the laser welding conditions was indispensable for the strong bonding with maintaining the shape of particles. Thus, the two-particle welding tests were preliminarily conducted. On the basis of this result, we successfully assembled the large-scale artificial crystals with diamond structure from the PE -ceramic or -carbon composite particles. In order to discuss applicability of the obtained crystals to terahertz (THz) wave photonic crystals, the transmittance spectrum of the crystals was evaluated by a THz wave time domain spectroscopy. The PE-ceramic particle crystal presented an ideal photonic band gap which perfectly agreed with the theoretical one.