An antenna system mounted in a portable terminal has a main antenna for transmitting and receiving a radio wave signal, wherein the main antenna is contained in a body of the portable terminal in a first mode of the portable terminal and is pulled out from a body of the portable terminal in a second mode of the portable terminal; and a sub-antenna for performing diversity reception of a radio wave signal, wherein when a state of the main antenna is switched depending on whether the portable terminal is in the first mode or the second mode, constitution of the main antenna and constitution of the sub-antenna are varied so that directivities of the main antenna and the sub-antenna compensate each other. Typically, the main antenna is a whip antenna having a helical antenna and a linear antenna, and a sub-antenna element is provided.