A bed-leaving sensor for detecting bed-leaving by a user on a bed, including: a sitting position detection member that detects a sitting position of the user based on a detection value of a pressure sensor arranged on the bed a foot movement detection member for detecting foot movement of the user based on the detection value of the pressure sensor and a bed-leaving behavior detection member that detects bed-leaving behavior of the user with the sitting position or the foot movement being detected within a preset bed-leaving expectation region as a condition.
