A fixed-pitch coaxial contra-rotating helicopter (1, 400), comprising: a rotor drive unit provided with an upper rotor and a lower rotor rotatable in opposite directions about a common axis of rotation; a slide unit attached to a bottom surface of the rotor drive unit for sliding the rotor drive unit in an orthogonal plane direction orthogonal to the axis of rotation; a lower airframe (5, 5A) hung from a bottom surface of the slide unit characterized in that the lower airframe (5, 5A) is hung from a bottom surface of the slide unit via a pivot joint, and in that the helicopter (1, 400) further comprises: at least two extensible links (17, 17A) bridging between the lower airframe (5, 5A) and the bottom surface of the slide unit; detectors attached to the links (17, 17A) for detecting amounts of extension of the links (17, 17A); and a control circuit for controlling a direction of slide and an amount of slide of the rotor drive unit by the slide unit, on the basis of detection output from the detectors; wherein on the basis of the amounts of extension of the links (17, 17A) detected by the detectors, in a case in which the rotor drive unit tilts about the pivot joint with respect to a direction of a center of gravity of the lower airframe (5, 5A), the control circuit slides the rotor drive unit in a direction in which the rotor drive unit is tilted, such that a vertical line that passes through the center of gravity of the lower airframe (5, 5A) moves in a direction in which it comes closer to a vertical line that passes through a center of thrust generated by the rotation of the upper rotor and the lower rotor. a rotor drive unit provided with an upper rotor and a lower rotor rotatable in opposite directions about a common axis of rotation; a slide unit attached to a bottom surface of the rotor drive unit for sliding the rotor drive unit in an orthogonal plane direction orthogonal to the axis of rotation; a lower airframe (5, 5A) hung from a bottom surface of the slide unit characterized in that the lower airframe (5, 5A) is hung from a bottom surface of the slide unit via a pivot joint, and in that the helicopter (1, 400) further comprises: at least two extensible links (17, 17A) bridging between the lower airframe (5, 5A) and the bottom surface of the slide unit; detectors attached to the links (17, 17A) for detecting amounts of extension of the links (17, 17A); and a control circuit for controlling a direction of slide and an amount of slide of the rotor drive unit by the slide unit, on the basis of detection output from the detectors; wherein on the basis of the amounts of extension of the links (17, 17A) detected by the detectors, in a case in which the rotor drive unit tilts about the pivot joint with respect to a direction of a center of gravity of the lower airframe (5, 5A), the control circuit slides the rotor drive unit in a direction in which the rotor drive unit is tilted, such that a vertical line that passes through the center of gravity of the lower airframe (5, 5A) moves in a direction in which it comes closer to a vertical line that passes through a center of thrust generated by the rotation of the upper rotor and the lower rotor. at least two extensible links (17, 17A) bridging between the lower airframe (5, 5A) and the bottom surface of the slide unit; detectors attached to the links (17, 17A) for detecting amounts of extension of the links (17, 17A); and a control circuit for controlling a direction of slide and an amount of slide of the rotor drive unit by the slide unit, on the basis of detection output from the detectors; wherein on the basis of the amounts of extension of the links (17, 17A) detected by the detectors, in a case in which the rotor drive unit tilts about the pivot joint with respect to a direction of a center of gravity of the lower airframe (5, 5A), the control circuit slides the rotor drive unit in a direction in which the rotor drive unit is tilted, such that a vertical line that passes through the center of gravity of the lower airframe (5, 5A) moves in a direction in which it comes closer to a vertical line that passes through a center of thrust generated by the rotation of the upper rotor and the lower rotor.