Magnetic field (B-field) is playing an important role in star formation. In the stand point of stability, mass-to-magnetic flux ratio, 2πG^{1/2}M/Φ, of the clouds/cloud cores is a key parameter controlling their evolution. B-field is important also in the angular momentum transfer by magnetic braking and by driving outflow. In this presentation, we focus on the fingerprint of B-field remained in the polarization of thermal emissions from magnetically aligned dust grains. For example, we can distinguish between a simple hourglass shape B-field and B-field which can drive outflows by transferring angular momentum. That is, using the polarization, we try to understand the three dimensional structure of B-field. Second example is the filamentary cloud which has lateral B-field and we consider its appearance in the polarization. We will discuss observational polarization signatures indicating massive and less massive filaments. Following characteristic points of polarization observation are useful to understand the 3D structure of filaments: (1) angle between polarization B-vector and the filament, (2) comparison of scaleheights determined from total intensity and polarized intensity, and (3) polarization degree.