The object of the present invention is to provide a mattress of a novel structure that can quickly perform dispersion of a body pressure acting part of a user, and can reduce discomfort felt by the user when doing a cell internal pressure switching operation, as well as a control method thereof. The present invention is provided with: a grouping step (S2) for, on the basis of a body pressure applied to each of a plurality of cells (24), dividing the plurality of cells (24) into groups a target internal pressure setting step (S3) for setting a target internal pressure of the cells (24) for each group divided at the grouping step (S2) and an internal pressure adjusting step (S4) for interconnecting the cells (24) in each group and adjusting the internal pressure of the cells (24) to the internal pressure set in the target internal pressure setting step (S3).
