A communication device includes: a reception antenna having element reception antennas, an element reception signal processor for processing element reception signals and outputting signals received from two directions changeable electronically and independently, a transmission antenna having element transmission antennas, an element transmission signal generator for generating element transmission signals capable of transmitting radio waves in two directions changeable electronically and independently, two modems for modulation and demodulation of transmission and reception signals using two communication lines, and a controller. The communication device operates by switching between a search mode to communicate by tracking a primary satellite and searching a direction at which beacon signals transmitted by satellites are receivable in a search range, and a two-line mode to communicate by tracking the primary satellite and the secondary satellite found in the search mode.