We present the sensitivity calculation results for observing the Cosmic Infrared Background (CIRB) by the Multi-purpose IR Imaging System (MIRIS), which will be launched in 2010 as a main payload of the Science and Technology Satellite 3 (STSAT-3). MIRIS will observe in I ($0.9{sim}1.2um$) and H ($1.2{sim}2.0um$) band with a $4{ imes}4$ degree field of view to obtain the large scale structure (${sim}3$ degree) of the CIRB. With the given specifications of the MIRIS, our sensitivity calculation results show that the MIRIS has a detection limit of ${sim}9;nW;m^{-2};sr^{-1}$ (I band) and ${sim}6;nW;m^{-2};sr^{-1}$ (H band), which is appropriate to observe the large scale structure of CIRB.