To easily deal with a case when water or the like is spilt on a chair, sofa or the like, and to prevent a covered material from absorbing a dust or the like.

A core body 2 is formed in such a way that cushion materials 4, 4 are bonded to an upper surface of a seat section and a front surface of a back section in a core material. When a chair having a structure covering an external surface of the core body 2 is formed, one part of the external surface of the cushion materials 4 is covered with water impermeable covering member 10 to prevent water from permeating into the cushion materials 4 even when water or the like is spilt. The covered material 6 is detachably attached to engagements 8k, 8j of the face fastener.