There is provided a horn device for a railcar capable of delivering horn sound to a long distance in a traveling direction and being less likely to spread sound in a car width direction. A horn device for a railcar according to one aspect of the present invention includes: a whistle portion that is supplied with compressed air to make horn sound in a traveling direction; a duct located in the traveling direction of the whistle portion and having an opening portion at an end portion in the traveling direction; and at least one partition plate that is disposed perpendicularly to a car width direction, extends in a car longitudinal direction, and divides the interior of the duct.