MAGnetic Data Acquisition System (MAGDAS) of the Circum-pan Pacific Magnetometer Network (CPMN) is introduced. MAGDAS/CPMN measures the ground magnetic field all around the world and sends the measured data to Space Environment Research Center (SERC), Fukuoka, Japan, via Internet, telephone line or satellite phone line. As examples of the phenomena observed by MAGDAS/CPMN, we present observations of the equatorial electrojet, Pi 2 waves near the dip equator, and SC-associated ionospheric electric field; Pi 2 is a transient ULF wave taking place at the beginning of a phenomenon called substorm, and SC (sudden commencement) is a phenomenon taking place as an interplanetary shock arrives at the Earth. We also compare ground-based estimations of the space plasma density with simultaneous direct observations by spacecraft.