An obstacle detection device for detecting an obstacle in the vicinity of a machine body of a construction machine and performing handling processing according to a result of the detection, the device comprising: an inclination information acquisition section configured to obtain inclination information that is information about a state of relative inclination of the machine body with respect to a surrounding ground area that is an area of the ground extending in the vicinity of a location ground area that is an area of the ground on which the construction machine is located; an area setting section configured to set a monitoring area in the vicinity of the machine body; an obstacle detection section configured to detect an obstacle within the monitoring area; and a handling processing section configured to perform predetermined handling processing upon detection of the obstacle by the obstacle detection section, wherein the area setting section is configured to modify the monitoring area according to the inclination information, and characterised in that the area setting section is configured to, in a first case where the inclination information indicates no inclination of the machine body with respect to the surrounding ground area, set the monitoring area to a predetermined reference area and, in a second case where the inclination information indicates that the machine body is inclined with respect to the surrounding ground area to a certain degree or more, if a predetermined inference condition for inferring that setting the monitoring area to the reference area will result in inclusion of at least part of the surrounding ground area in the monitoring area is satisfied, change the monitoring area to an area that remains when a portion of the reference area close to the surrounding ground area is removed from the reference area so that the surrounding ground area is excluded from the set monitoring area, and if the inference condition fails to be satisfied, set the monitoring area to the reference area. an inclination information acquisition section configured to obtain inclination information that is information about a state of relative inclination of the machine body with respect to a surrounding ground area that is an area of the ground extending in the vicinity of a location ground area that is an area of the ground on which the construction machine is located; an area setting section configured to set a monitoring area in the vicinity of the machine body; an obstacle detection section configured to detect an obstacle within the monitoring area; and a handling processing section configured to perform predetermined handling processing upon detection of the obstacle by the obstacle detection section, wherein the area setting section is configured to modify the monitoring area according to the inclination information, and characterised in that the area setting section is configured to, in a first case where the inclination information indicates no inclination of the machine body with respect to the surrounding ground area, set the monitoring area to a predetermined reference area and, in a second case where the inclination information indicates that the machine body is inclined with respect to the surrounding ground area to a certain degree or more, if a predetermined inference condition for inferring that setting the monitoring area to the reference area will result in inclusion of at least part of the surrounding ground area in the monitoring area is satisfied, change the monitoring area to an area that remains when a portion of the reference area close to the surrounding ground area is removed from the reference area so that the surrounding ground area is excluded from the set monitoring area, and if the inference condition fails to be satisfied, set the monitoring area to the reference area.