To provide a one-piece type swimming suit readily put on and taken off, and preventing sensible temperature for a wearer when being in activity in water or at waterfront from getting lower.

This one-piece type swimming suit is structured as follows: a swimming suit body is made of a complex material comprising a heat insulating sheet and woven fabrics laminated on both surfaces of the heat insulating sheet directly or via a reflection film layer intervening therebetween, a cut part longitudinally ranging from the upper end of the swimming suit body to the navel part at most or the same level is formed at the front part or the side part, a longitudinal fastener stretchable along its full length is attached to the cut part so as to make the swimming suit openable.