Possibility of damage of a rotary damper is reduced even when rotating force larger than an assumption is applied. The rotary damper comprises: the case 11 having the cylindrical chamber 111; the rotor 12 housed in the cylindrical chamber 111; the viscous fluid 13 filling the cylindrical chamber 111; the check valve 15; and the pressure-regulating valve 16. In the cylindrical chamber 111, the projecting bulkheads 115a, 115b are formed. The rotor 12 comprises: the rotor body 121 and vanes 124a, 124b. The check valve 15 closes when the rotor 12 rotates in the normal rotation direction, so as to restrict movement of the viscous fluid 13 between areas 111a - 111d partitioned by the bulkheads 115a, 115b and the vanes 124a, 124b. On the other hand, the check valve 15 opens when the rotor 12 rotates in the reverse rotation direction, so as to allow movement of the viscous fluid 13 between the areas 111a - 111d. The pressure-regulating valve 16 opens when rotating force applied for rotating the rotor 12 in the normal rotation direction is above a predetermined value, to cancel the restriction of movement of the viscous fluid 13 between the areas 111a - 111d.
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