A threat detecting technique is provided capable of efficiently harvesting an inspection sample for threat detection from an inspection object. The sample-harvesting sheet for harvesting the sample from the inspection object has a portion formed with a plurality of recesses in the plane of the sheet. The portion is moved relatively in a state in contact with the sample-harvesting object of the inspection object, thereby transferring the inspection sample deposited on the sample-harvesting object to the recesses and retaining it therein.