  We have measured the magnetization of the organic compound BIP-BNO
(3,5'-bis(N-tert-butylaminoxyl)-3',5-dibromobiphenyl) up to 76 T where the
magnetization is saturated. The S = 1/2 antiferromagnetic Heisenberg two-leg
spin-ladder model accounts for the obtained experimental data regarding the
magnetization curve, which is clarified using the quantum Monte Carlo method.
The exchange constants on the rung and the side rail of the ladder are
estimated to be J(rung)/kB = 65.7 K and J(leg)/kB = 14.1 K, respectively,
deeply in the strong coupling region: J(rung)/J(leg) > 1.
