Disclosed is a door damper, in which a safety check valve is installed in consideration of the case in which an impact exceeding a design pressure will be applied, thereby absorbing the impact to enable a door to be closed safely and smoothly. In the door damper, a safety check valve is installed in a piston, and thus is opened in cooperation with another check valve installed between a spring holder and the piston when the pressure exceeding a design pressure is applied. Thereby, when the impact exceeding the design pressure occurs, the safety check valve can absorb the impact to prevent damage. A channel can be adjusted by only ridges formed on an outer circumference of the check valve, so that productivity can be improved thanks to easy tolerance management. Further, an oil seal is not contracted or deformed in spite of long-term use.