A drowsiness detection device includes a memory; and a processor coupled to the memory and the processor configured to calculate a respiration variation period based on heartbeat interval data which is generated based on data that is obtained from a heartbeat sensor; predict a subsequent period structure of the respiration variation based on the calculated respiration variation period; determine whether or not an abnormal signal is mixed in the heartbeat interval data by comparing the heartbeat interval data during sequential update and the predicted subsequent period structure; and replace the respiration variation period which corresponds to the heartbeat interval data that includes the abnormal signal with the predicted subsequent period structure in a case where it is determined that the abnormal signal is mixed.