A bed apparatus includes: a mattress mounted on a bed body； and, first cells arranged on both left and right sides in a longitudinal direction of the bed body and is configured to change the body position of a patient on the mattress by inflating the first cells alternately. When the first cells on the left and right sides are inflated, and when a difference in pressure between the first cells on the left and right sides has continuously fallen within a decision pressure value range for a decision pressure value continuation time, the body position of the patient is changed, whereas when the difference has not continuously fallen within the pressure value range for the continuation time or when the difference has continuously fallen out of the pressure value range for the continuation time, change of the body position of the patient will not be performed.
