We have developed a Stokes polarimeter system which can be used at an arbitrary, wide terahertz frequency region by using a wave plate and difference frequency generation system with DAST crystal (DAST-DFG). Conventional wave plates made of dielectric materials with intrinsic birefringence at optical wavelengths cannot be applied directly to terahertz frequencies because of the large absorption loss. High resistivity silicon, which remains transparent even at the higher terahertz frequency region, was selected as the wave plate material. Although the silicon has intrinsic birefringence hardly, large form birefringence can be successfully induced by fabricating a one-dimensional grating structure of subwavelength scale on its surface and proper operation as wave plate can be confirmed. By using the wave plate with a polarizer on DAST-DFG system, Stokes polarimeter system can be also successfully developed. Our approach can be extended to an arbitrary, wide terahertz frequency region and open many terahertz-wave applications associated with polarization physics at there.