A dust collection system, a dust collection method, and a dust collector, can enhance dust-collecting efficiency while reducing the volume of the dust collector as a whole. A dust collector is provided with a casing having an inlet into which gas is introduced; a discharge electrode to which voltage is applied, the discharge electrode being disposed inside the casing and having a spike called discharge spike and mounting frames for supporting the discharge spike; and a collecting electrode having a planar member, disposed inside the casing facing the discharge electrode, the mounting frames being inclined with relation to the gas flow at the inlet. Two mounting frames are connected to each other on the downstream side of the gas flow, and are arranged so that, between the two mounting frames, the upstream side of the gas flow is wider than the downstream side of the gas flow.