Patent ID: 7330729

Claim:
A positional information system comprising: a mobile terminal device, comprising: a positional information acciuisition unit for acquiring positional information, which is information of the current location; a user interface unit for displaying said positional information; a power supply unit for supplying power to said positional information acquisition unit and said user interface unit; and a wireless unit for transmitting information to and receiving information from the outside; a geomagnetic sensor for detecting geomagnetism; and a control unit for comparing the output value of said geomagnetic sensor with a first set value that has been set in advance; determining that said mobile terminal device is stationary when the output value of said geomagnetic sensor continues to be less than said first set value for at least a first set time period that has been set in advance; and determining that said mobile terminal device is moving when the output value of said geomagnetic sensor fluctuates by at least said first set value, wherein said control unit: makes the period of executing a positional information acquisition process for acquiring positional information longer than a reference period that has been set in advance when said mobile terminal device is stationary, and makes said period of executing said positional information acquisition process shorter than said reference period when said mobile terminal device is moving, causes a halt of the supply of power from said power supply unit to said positional information acquisition unit and said user interface unit when the output value of said geomagnetic sensor continues to be a value that is smaller than said first set value for a time period that is equal to or greater than a second set time period that has been set in advance in addition to said first set time period; and a base station that holds a first set value that is set in advance in accordance with the geomagnetic strength in its own vicinity and that transmits said first set value to said mobile terminal device, the base station comprising: means for outputting a moving state of said mobile terminal device to a caller who is currently engaged in a call to said mobile terminal device, when said caller outputs a mobile terminal device movement enquiry request, wherein the call between said caller and said mobile terminal device is capable of being changed from speech communications to character communications between said caller and a user of said mobile terminal device, based on a conversion made by a communications device of said caller under control of said caller, wherein character communications is made instead of speech communications when the mobile terminal device is determined to be moving at a high rate of speed.