We measured the temperature dependence of the magnetic susceptibility and specific heat and the magneticfield dependence of the magnetization of CuInVO5. An antiferromagnetically ordered state appears below T-N = 2.7 K. We observed a 1/2 quantum magnetization plateau above 30 T at 1.3 K. We consider that the probable spin model for CuInVO5 is an interacting spin-1/2 tetramer model. We evaluated values of the intratetramer interactions as J(1) = 240 +/- 20 K (antiferromagnetic) and J(2) = -142 +/- 10 K (ferromagnetic). The ground state of the isolated spin tetramer with the J1 and J2 values is spin singlet. The shrinkage of ordered magnetic moments by quantum fluctuation can be expected. Detectable low-energy longitudinal-mode magnetic excitations may exist in CuInVO5.