There is disclosed a portable GPS (Global Positioning System) receiver carried by a user. The receiver measures the distance traveled by the user and the speed. In the prior art technique, if satellites cannot be captured, no measurements are made. To find the distance and speed accurately, the measurements have to be performed continuously, thus increasing the electric power consumed by the receiver. The inventive receiver once finds the speed from the Doppler frequencies of the carrier waves. Then, a first distance-calculating means finds the distance from the speed. A walk-detecting means detects walking. A step number-calculating means accumulates the number of steps taken in steps. A stride-calculating means finds the stride from the accumulated step number and from the found distance. Then, a second distance-calculating means finds the distance from the stride and from the accumulated number of steps. A speed-calculating means finds the speed. The GPS receiver receives at regular intervals and updates the stride.