To obtain a process oil having a reduced content of polycyclic aromatic compounds accused of being a hazard to human bodies while retaining other properties.

This process oil has a polycyclic aromatic compound content of less than 3 wt.%, an aromatic compound content of at least 25 wt.%, a kinetic viscosity of 10-30 mm2/s at 100°C, a 5 vol.% running point of 370-530°C and a density of 0.870-0.970 g/cm3. The process oil is prepared by subjecting to extraction with a polar solvent a mixed oil comprising 40-97% of the extract obtained from a mineral oil by the extraction with a polar solvent and 30-60% of a lubricant base oil thereby reducing the polycyclic aromatic compound content to less than 3 wt.%.