A fuel pump has substantially coaxial outer and inner pump chambers. An impeller has partition walls correspondingly to the inner pump chamber to define inner vane grooves. A rear surface is located at a rear side in a rotative direction of each inner vane groove. At least a radially inner side of the rear surface inclines rearward in the rotative direction from the radially inner side to a radially outer side. A first line connects a radially inner end of the rear surface with a radially outer end of the rear surface. A second line radially extends from the radially inner end of the rear surface. The first line and the second line therebetween define a backward tilt angle α2, which satisfies a relationship of 30°≦α2≦80°.