The microscopic dynamics of oblate-prolate shape coexistence/mixing phenomena in (68) Se and Kr-72 are studied by means of the adiabatic self-consistent collective coordinate (ASCC) method in conjunction with the pairing-plus-quadrupole (P + Q) Hamiltonian, including the quadrupole pairing interaction. A quantum collective Hamiltonian is constructed, and excitation spectra, spectroscopic quadrupole moments and quadrupole transition properties are evaluated. The effect of the time-odd pair field on the collective mass (inertia function) of the large-amplitude vibration and the rotational moments of inertia about three principal axes is evaluated. It is found that the basic properties of the shape coexistence/mixing are qualitatively reproduced. The results of the calculation indicate that the oblate-prolate shape mixing decreases as the angular momentum increases.