To provide a GPS (global positioning system) receiver, a program, and an information storage medium, capable of measuring its present position simply and accurately by using signals from two GPS satellites.

This GPS receiver 20 is provided with a receiving part 22 for receiving satellite signals from the GPS satellites, a control part 23 for causing the receiving part 22 to receive the satellite signals, an updating part 26 for updating satellite data 31 used in positioning computation based on the received satellite signals, and a positioning/computing part 28 for finding a present position based on the satellite data 31. At a first point of time, satellite signals are received from two GPS satellites, and first and second groups of data are stored as part of the satellite data 31. At a second point of time when a prescribed length of time has elapsed from the first point of time, satellite signals from the two GPS satellites are received, and third and fourth groups of data are stored as part of the satellite data 31. A present position is found based on the first to fourth groups of data.