An air conditioner includes a flow path through which air to be humidified flows, an agitating plate group, and a spray nozzle. The agitating plate group is configured by arranging agitating plates in parallel at intervals over an entire cross-section of the flow path. Each of the agitating plates has a plate width adjusted to cause a vortex downstream. The spray nozzle is disposed immediately downstream of the agitating plate group, and sprays water particles in a direction perpendicular to a flow direction of the flow path. The plate width of each of the agitating plates is adjusted to satisfy a range of a Reynolds number causing a Karman vortex within a range of used wind speeds. The air conditioner provides high humidification efficiency and high saturation efficiency.