One quarter of the energy density of our universe is composed of dark matter, whereas the particle nature of it is still mysterious. In recent years, motivated by a variety of unexplained astronomical signatures, the paradigm of weakly interacting dark matter supplied by a new long range force in the dark sector came to prominence. The simplest way to realize such a dark force is to introduce a light vector boson, the dark photon, in the dark sector. If the dark photon is light enough itself, it can also be a candidate of dark matter. In this talk, the speaker will focus on the physical consequences induced by the dark photon and how to search for it with current experiments.