A periodical signal is transmitted from a cellular base station. A memory circuit having a capacity of the signal for one cycle is provided. Newly received information is added to information previously accumulated in the memory circuit, and the resultant information is again accumulated in the memory circuit, thereby enabling the received information to be stored in the memory circuit having the capacity for only one cycle of the signal. Conventionally, a large amount of memory has been required to perform coherent adding for a long time period, whereas the present invention can reduce the circuit scale and the amount of memory, and also reduce the number of times of operations required for the long-period coherent adding, when a mobile station is located using a cellular communication system.