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 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 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 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. <EOS>