In this presentation, we will discuss that the collisions of dense cores frequently happen in star-forming regions, particularly in cluster-forming and high-mass star-forming regions. Then, we carry out the hydrodynamic numerical simulations of core collision, showing that asymmetric structures observed in protostellar cores, e.g., streamers, can be created by such collisions. The collision basically creates the rotating disk around protostars with a prominent arm. The structure formation depends on the parameters such as an impact parameter and collision speed. For faster collision, a companion star forms in a shock-compressed layer. The infall motions are also observed along the arms and streamers. We briefly compare the images of the observations with numerical results.