This paper summarizes the development of "probe-vehicle" system for advanced railway condition monitoring. We developed a portable condition monitoring system for track which is easily set on in-service vehicle. In this system, irregularities of rail are estimated from vertical and lateral acceleration of car body. A roll angle of car body, which is calculated using a rate gyroscope, is used to distinguish irregularity of line from irregularity of level. Rail corrugation can be detected from cabin noise with spectral peek calculation. GPS system and map matching algorithm localizes the fault on track. Experiments using in-service vehicle were carried out to evaluate the developed system. The results show that the condition of rail irregularity and rail corrugation can be estimated effectively. It is also shown that the system can be applicable for monitoring driver's operation condition. (6 pages)