A mixing device of the present invention includes a mixing section for mixing a liquid-phase fluid with one or two or more of a solid, a gas, and a liquid-phase fluid other than the aforementioned liquid-phase fluid, wherein the mixing section includes a fluid supply hole, a fluid discharge hole, a passage communicating with the supply hole and the discharge hole, and a plurality of pins protruding from the passage, and a fluid containing a material to be mixed is supplied from the supply hole to the passage, is mixed by passing through the passage and coming into contact with the pins, and is discharged from the discharge hole.