A flexible synthetic resin tube is provided by uniting an inner layer of a polyether-series thermoplastic polyurethane resin with a hard synthetic resin spiral reinforcement (e.g. a hard vinyl chloride resin) or a soft synthetic resin outer layer (e.g. a soft vinyl chloride resin), through an interposed adhesive intermediate resin layer. The polyurethane resin includes a resin having a diol composed of a tetramethylenoxy unit as a polyol component. The spiral reinforcement may be buried in the outer layer. The intermediate resin layer may comprise a mixture of the polyether-series thermoplastic polyurethane resin, and the synthetic resin for the spiral reinforcement or the outer layer. This tube imparts an enhanced hydrolysis-resistant property to the polyurethane resin forming the inner layer, and an improved adhesive strength between the inner layer and the spiral reinforcement or the outer layer.