We performed MHD simulations of the contraction of rotating, magnetized molecular cloud cores. In the molecular cores, B-field and angular momentum (J) vector are not always aligned. When a first hydrostatic core forms, axisymmetric structure appears and average B and J are parallel in small scale. However, in large scale, the configuration is far from this. This means that contraction process is imprinted on the snapshot. We calculated two mock observations of MHD simulations (1) the polarization of dust thermal emission to reveal the magnetic evolution and (2) the line emissions from interstellar molecules to reveal the evolution of density and velocity. Comparing the mock observations with true ones, we can answer several questions: in which case the hourglass-shaped and S-shaped magnetic fields are seen; how the distribution of polarized intensity is understood; how the first hydrostatic core should be observationally identified.