A sensor includes: a living body component extractor that receives a signal transmitted from each transmitting station and influenced by a living body, and extracts a signal component influenced by the living body; a position spectrum function calculator that calculates as many position spectrum functions as the number of combinations of transmitting stations and receiving stations, the position spectrum functions each being calculated from the signal component and corresponding to a likelihood of a position of the living body; a weight function calculator that calculates as many weight functions as the number of combinations, the weight functions each representing reliability of a position spectrum function; an integrated position spectrum function calculator that outputs an integrated position spectrum function using the position spectrum functions and the weight functions; and a position estimator that estimates the position of the living body by detecting a maximum value from the integrated position spectrum function.