A warning output device includes a rear sensor unit and an electronic control unit. The electronic control unit is configured to, when a shift position is an R range, based on information from the sensor unit indicating that a first obstacle is detected, output a warning for informing an occupant of the presence of the first obstacle, in a first state, output first predetermined warning display and first predetermined warning sound; and in a second state, output second predetermined warning display and second predetermined warning sound. The ECU is configured to, 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.