A mattress including: a support surface to support a user； a mattress main body that constitutes the support surface； at least one pressure sensor having a flexible sheet shape to detect a pressure acting on the support surface； a support surface cover positioned with respect to the mattress main body and arranged so as to cover the support surface； and at least one positioning member provided to the support surface cover to permit a movement of the pressure sensor with respect to the support surface cover in a planar direction while limiting an amount of the movement of the pressure sensor with respect to the support surface cover in the planar direction such that the pressure sensor is positioned on the support surface by the positioning member.
