Abstract: A fire sensing device for actuating associated fire alarm system having a heat receiving plate member of improved heat receiving efficiency for rapidly transmitting any abnormal heat received from environmental atmosphere to a heat-responsive switching means thermally connected to the plate member to actuate the alarm system promptly and reliably is provided. In order to enlarge surface area, the heat receiving plate member has many fins comprising elongated bridging parts defined by adjacent ones of many parallel slits made in the plate member and twisted about elongated axis preferably by an angle of 40.degree. to 60.degree. with respect to the plane of the plate member so as to be raised at both longitudinal edges from the member on its both sides, whereby abnormally heated air passing along a surface or surfaces of the plate member is caused to flow along the fins through or into the slits to rapidly and efficiently transmit its heat to the plate member.