We investigated the magnitude-phase relation of (162173) 1999 JU3, a target asteroid for the JAXA Hayabusa 2 sample return mission. We initially employed the International Astronomical Union's H-G formalism but found that it fits less well using a single set of parameters. To improve the inadequate fit, we employed two photometric functions: the Shevchenko and Hapke functions. With the Shevchenko function, we found that the magnitude-phase relation exhibits linear behavior in a wide phase angle range ( alpha = 5degrees-75degrees) and shows weak nonlinear opposition brightening at alpha < 5degrees, providing a more reliable absolute magnitude of Hv = 19.25 + or - 0.03. The phase slope (0.039 + or - 0.001 mag deg super(-1)) and opposition effect amplitude (parameterized by the ratio of intensity at alpha = 0degrees.3 to that at alpha = 5degrees, I(0.degrees3)/I(5degrees) = 1.31 + or - 0.05) are consistent with those of typical C-type asteroids. We also attempted to determine the parameters for the Hapke model, which are applicable for constructing the surface reflectance map with the Hayabusa 2 onboard cameras. Although we could not constrain the full set of Hapke parameters, we obtained possible values, w = 0.041, g = -0.38, B sub(0) = 1.43, and h = 0.050, assuming a surface roughness parameter theta = 20degrees. By combining our photometric study with a thermal model of the asteroid, we obtained a geometric albedo of p sub(v) = 0.047 + or - 0.003, phase integral q = 0.32 + or - 0.03, and Bond albedo A sub(B) = 0.014 + or - 0.002, which are commensurate with the values for common C-type asteroids.