A warning output device (1; 1A) comprising: a sensor unit configured to detect a first obstacle behind a host vehicle; and an electronic control unit (40; 40A) configured to: when a shift position is an R range, output a warning for informing an occupant of the presence of the first obstacle based on information from the sensor unit indicating that the first obstacle is detected; in a first state in which the first obstacle is present within a first predetermined area behind the host vehicle, output first predetermined warning display and first predetermined warning sound, characterized in that the electronic control unit (40, 40A) is further configured to in a vehicle stop state and a second state in which the first obstacle is not present within the first predetermined area and the first obstacle is present within a second predetermined area behind the host vehicle farther from the host vehicle than the first predetermined area, output second predetermined warning display and second predetermined warning sound; and in the second state, output the second predetermined warning sound for a predetermined time, then stop the output of the second predetermined warning sound, and output the second predetermined warning display for a longer time than the second predetermined warning sound. a sensor unit configured to detect a first obstacle behind a host vehicle; and an electronic control unit (40; 40A) configured to: when a shift position is an R range, output a warning for informing an occupant of the presence of the first obstacle based on information from the sensor unit indicating that the first obstacle is detected; in a first state in which the first obstacle is present within a first predetermined area behind the host vehicle, output first predetermined warning display and first predetermined warning sound, characterized in that the electronic control unit (40, 40A) is further configured to in a vehicle stop state and a second state in which the first obstacle is not present within the first predetermined area and the first obstacle is present within a second predetermined area behind the host vehicle farther from the host vehicle than the first predetermined area, output second predetermined warning display and second predetermined warning sound; and in the second state, when a shift position is an R range, output a warning for informing an occupant of the presence of the first obstacle based on information from the sensor unit indicating that the first obstacle is detected; in a first state in which the first obstacle is present within a first predetermined area behind the host vehicle, output first predetermined warning display and first predetermined warning sound, characterized in that the electronic control unit (40, 40A) is further configured to in a vehicle stop state and a second state in which the first obstacle is not present within the first predetermined area and the first obstacle is present within a second predetermined area behind the host vehicle farther from the host vehicle than the first predetermined area, output second predetermined warning display and second predetermined warning sound; and in the second state, output the second predetermined warning sound for a predetermined time, then stop the output of the second predetermined warning sound, and output the second predetermined warning display for a longer time than the second predetermined warning sound.