Compton scattering hard X-ray source which consists of an X-band (11.424 GHz) electron linear accelerator and YAG laser is under construction at Nuclear Professional School, the University of Tokyo (UTNS). Monochromatic hard X-rays are required for variety of medical and biological applications. Our scheme of the hard X-ray source is to produce a monochromatic hard X-ray via collision between 35 MeV electron beam and 2.5 J/10 nsec Nd : YAG laser. In order to increase the efficiency of the X-ray yield, we adopt a laser pulse circulation system. In our case, the laser pulse circulation system can increase the X-ray intensity of up to 50 times. Main features of our scheme are to produce monochromatic tunable hard (10-40 keV) X-rays with the intensities of 108-109 photons/sec. In addition, X-ray energy can be changed with rapidly by 40 ms by introducing two different wavelength lasers (YAG fundamental (1064 nm), 2nd harmonic (532 nm)) and optical switch. This quick energy change is indispensable to living specimens and very difficult by a large SR light source and others. We designed a laser pulse circulation system to increase the X-ray yield 10 times higher (up to 108 photons/RF pulse, 109 photons/sec). It can be proved that the laser total increases 10 times higher by principle experiment with lower energy laser (25 mJ/pulse). Dual-energy X-ray CT and subtraction X-ray CT are available to determine 3D distribution of atomicc number density and electron density, and specified atomic distribution, respectively. Here, the construction status of the X-band beam line and the application plan of the hard X-ray will be reported.