Observational response of MAXI onboard ISS

The current status is reported of the development of Monitor of All-sky X-ray Image and the measurement of its observational response. MAXI is a scanning X-ray camera to be attached to the Japanese Experiment Module of the International Space Station in 2008. MAXI is mainly composed of two kinds of instruments, GSC which is sensitive to the 2 - 30 keV photons, and SSC to the 0.5 - 10 keV ones. As an X-ray all-sky monitor, MAXI has an unprecedented sensitivity of 7 mCrab in one orbit scan, and 1 mCrab in one week. Using the engineering mode of the proportional counter and of the collimator for GSC, the observational response of GSC is extensively measured. The acceptable performances are obtained as a whole for both the collimator and the counter. The engineering models of the other part of MAXI are also constructed and the measurement of their performance is ongoing.