A body movement detection sensor to be worn on a chest region comprising: a case; an annular part; a sensor section having a piezoelectric film and a circuit section, and; a right belt member extending from a right side of the sensor section; a left belt member extending from a left side of the sensor section; and an engagement member for engaging an open-end portion of the right belt member and an open-end portion of the left belt member with each other; wherein the piezoelectric film is configured to exhibit piezoelectric effect in a length direction, the right belt member and the left belt member have substantially no elasticity, and the body movement detection sensor further comprises an elastic sheet directly or indirectly connected to the right belt member and the left belt member, and a coupling part to which one end portion of the elastic sheet is coupled, wherein the case houses the piezoelectric film, the elastic sheet, the coupling part and the circuit section, one end portion of the piezoelectric film is coupled to the coupling part and the other portion of the piezoelectric film is coupled to the circuit section, wherein the circuit section is fixed to the case; the elastic sheet has one end portion coupled to the coupling part and the other end portion coupled to the annular part; the right belt member is arranged so as to be inserted through the annular part;on both sides of the case, a pair of holes for movability are formed through which the annular part is inserted, such that the annular part is slidable in the length direction along with expansions and contractions of the elastic sheet; and wherein the elastic sheet has a maximum amount of expansion larger than an amount of change of a thorax during breathing, has a length equal to or smaller than one-sixth of a total length of the right belt member and the left belt member, and is arranged so as to be within a range in front or back of the chest region of a wearer. a case; an annular part; a sensor section having a piezoelectric film and a circuit section, and; a right belt member extending from a right side of the sensor section; a left belt member extending from a left side of the sensor section; and an engagement member for engaging an open-end portion of the right belt member and an open-end portion of the left belt member with each other; wherein the piezoelectric film is configured to exhibit piezoelectric effect in a length direction, the right belt member and the left belt member have substantially no elasticity, and the body movement detection sensor further comprises an elastic sheet directly or indirectly connected to the right belt member and the left belt member, and a coupling part to which one end portion of the elastic sheet is coupled, wherein the case houses the piezoelectric film, the elastic sheet, the coupling part and the circuit section, one end portion of the piezoelectric film is coupled to the coupling part and the other portion of the piezoelectric film is coupled to the circuit section, wherein the circuit section is fixed to the case; the elastic sheet has one end portion coupled to the coupling part and the other end portion coupled to the annular part; the right belt member is arranged so as to be inserted through the annular part;on both sides of the case, a pair of holes for movability are formed through which the annular part is inserted, such that the annular part is slidable in the length direction along with expansions and contractions of the elastic sheet; and wherein the elastic sheet has a maximum amount of expansion larger than an amount of change of a thorax during breathing, has a length equal to or smaller than one-sixth of a total length of the right belt member and the left belt member, and is arranged so as to be within a range in front or back of the chest region of a wearer.