Drag reduction of the pipe flow using flexible tubes was experimentally examined in comparison with that using rigid tube. The coefficient of friction in the flexible tube is smaller than that in the rigid tube even if the variation of the cross section accompanied with the flow in the flexible tube is considered. The thinner the flexible tube and the larger the Reynolds number, the larger the rate of decrease of the coefficient of friction. In the case of the thinnest flexible tubes, it becomes about 22% at Re=3.0×104. These results are related to the power spectrum distribution of the pressure fluctuation.