A sensor includes: a correlation matrix calculator which calculates a correlation matrix from biological information extracted using reception signals obtained by receiving, in a predetermined period, signals transmitted to a predetermined space; a first number information calculator which calculates first number information; a MUSIC spectrum calculator which estimates a candidate of a position of at least one living body and outputs a likelihood spectrum; and a second number information calculator which estimates a position or second number information, which is a total number of living bodies with an increased degree of likelihood, from first position information possibly including a plurality of position candidates.