Cu-63 NMR measurements for the ladder sites on single crystals Sr14-xCaxCu24O41 (x = 9, 11.5), which consist of simple chains and 2-leg ladders of Cu2+ ions, have been carried out at f = 125.1 MHz for H parallel to b-axis. From respective measurements of the Knight shift and the nuclear spin-lattice relaxation rate, 1/T-1, the spin gap in the ladder has been found to be as large as Delta = 250 K (260 K) and 340 K (360 K) for x = 11.5 (x = 9), respectively.