1 Introduction

The JEM (Japanese Experiment Module) is a multi-purpose experiment facility for space science and technology on the International Space Station (ISS). JEM consists of a pressurized module and an Exposed Facility (EF). MAXI is the first astrophysical experiment selected for JEM-EF (Matsuoka 1997). MAXI is an X-ray all-sky-monitor and its main scientific objective is to study medium-long term variations of AGNs, and to watch Galactic transients (Matsuoka et al. 1997; Kawai et al. 1997). In addition to these, its sensitivity is good enough to detect GRB afterglows in the early phase of the decay. This paper describes the MAXI experiment and discusses its expected capability of the afterglow observation.