The Galactic Exoplanet Survey Telescope (GEST)

A portable telephone set having a ringing circuit for producing different ringing tones depending upon the use mode of the portable telephone set, a portable mode or a mobile mode. The ringing circuit comprises a mode detecting circuit for detecting the use mode, an internal loudspeaker housed in a housing of the portable telephone set for producing a first ringing signal when the portable telephone set is in the portable mode, an external loud-speaker connected externally of the housing for producing a second ringing signal when it is in the mobile mode and a ringing tone generator for generating a first and a second ringing tones for driving the respective loud-speakers producing first and second ringings. The first and second ringing tones have frequency spectra compatible with frequency characteristics of these loudspeakers to produce the respective ringings efficiently. The ringing signal generator may be a single ringing tone generating circuit producing two kinds of ringing tone or may be comprised of two different ringing tone generating circuits.