We propose a high performance ROIC for IR image sensor applications. Because a micro bolometer image sensor, used in an IR image sensor, is made by a MEMS process, the resistance of bolometers by each process does not appear same value under same IR energy incident condition. This resistance variation generates a different output signal for same input by each chip. Instead of a single input mode, we used a differential input mode to the proposed ROIC and thus, a new circuit structure that has high immunity to the process variations of micro bolometer was invented. This result is due to the characteristics of the differential input mode that suppress the commonly appeared error and amplify the differentially applied signal. Using results from a computer simulation, improvement such as that the effect of the process error on the bolometer's resistance was decreased 10-12% without an additional compensation circuit was found. Moreover we had analyzed the results by numerical methods and found that it is possible to control the gain and compensation ability by design the capacitors of the integrator appropriately. A full chip including a ROIC and a micro bolometer with 16×16 cell arrays was designed and implemented in standard 0.25um CMOS process.