A load measuring unit detects the load of a bed section and generates a load signal. A body weight computing unit computes the body weight of a user positioned on the bed section on the basis of the load signal. A first determination unit determines whether the body weight is equal to or less than a prescribed threshold. A center-of-gravity position computing unit computes a center-of-gravity position of the user on the basis of the load signal. A second determination unit determines whether the center-of-gravity position is in a monitored area of the bed section. The state of the user is detected to away from the bed when the first determination unit has determined that the body weight is equal to or less than a prescribed threshold, and the second determination unit has determined that the center-of-gravity position is within the monitored area.