Abstract: The present invention relates to a supply system for pre-treating a petroleum distillation residual oil to be fed to a hydrogenation apparatus. In order to remove iron fine particles having a particle size of less than 25.mu. in the feed oil which could be not removed in the prior art, by constituting a system comprising a heater for heating the feed oil to a given temperature by heat exchange with a high temperature bottom oil of a fractionating tower after hydrogenation treatment of the feed oil, a filter equipped with a back washing mechanism for filtering solid materials in the feed oil after heating, and a high gradient magnetic separator for magnetically separating magnetic iron fine particles having a particle size of less than 25.mu. contained in the feed oil.