We have studied experimentally and theoretically the system with a superconducting coplanar waveguide resonator coupled to normal-metal―insulator―superconductor junctions and a transmission line. The bias voltage across the junctions can enhance the photon-assisted electron tunneling across the junctions and be used to control the photon-absorption rate in the resonator. Our reflection measurement for coherent photon injected from the transmission line to the resonator reveals the remarkable controllability of the effective electromagnetic property of the system seen by the coherent photons. The measured effective q-factors are shown as a function of the bias voltage.