A flush toilet deodorizing device includes an intake port part forming an intake port intaking air; an exhaust port part forming an exhaust port exhausting deodorized air; a fan device provided in a deodorizing air channel, the deodorizing air channel linking the intake port and the exhaust port and allowing air to flow; a water deodorizing part provided in the deodorizing air channel, the water deodorizing part using water to deodorize a suctioned air; and an oxidation catalyst provided in the deodorizing air channel.