A nanowire optical device includes: a photonic crystal body having a planar shape and provided on a base part; an optical waveguide by a line defect in which a plurality of defects including a part without grating elements of the photonic crystal body are linearly arrayed; a trench formed in a waveguide direction in the optical waveguide; a nanowire made of a semiconductor and arranged in the trench; an n-type region formed on one end side of the nanowire; a p-type region formed on the other end side of the nanowire; an active region provided to be interposed between the n-type region and the p-type region in the nanowire; a first electrode connected to the n-type region; and a second electrode connected to the p-type region.