This paper describes quantitative nondestructive evaluations of wall thinning in power plants by electro-magnetic acoustic transducers (EMAT). Among Japan's aging plants, their inspections and costs are increasing. Therefore, Interest is currently focused on continuous monitoring to the plants in operation. Inspection using EMAT is suitable for the continuous monitoring, because EMAT itself is attracted on the pipe. In this paper, we tested corrosion shapes of straight pipes which were machined to simulate flow-accelerated corrosions. Additionally, we measured thicknesses of an elbow pipe. The measured values gave close agreement with the observed values which were measured by an ultrasound thick gauge. We confirm that EMAT has the capability to measure thicknesses of corrosion wastages of the pipes.