To improve the cold storage performance by preventing intrusion of outer air, leakage of chill through a thermally insulated sliding door arranged on the back side of a case body as well as dew formation.

A thermally insulated sliding door 6 comprising sliding doors 6A, 6B is provided at the opening on the back of a case body 1 provided with a double swing doors on the front and E-shaped rails 7 having two rail grooves at the upper and lower ends is laid at the upper and lower ends thereof in order to guide and support the sliding door in the opening/closing direction. In such a reach-in type refrigerated showcase, the sliding door 6A is applied with a gasket 8 along the rear side at the side edge of a sash 6a in order to choke a gap occurring at the overlapped part of the sliding doors 6A, 6B when the thermally insulated door is closed. Furthermore, the upper and lower rails are provided, respectively, with a tip packing 9 stretching back and forth at the forward end of a center rib 7a along the longitudinal direction thereof in order to choke the gap between the sliding door and the rail thus preventing intrusion of outer air, leakage of chill and dew formation.