A vehicle lamp washer system comprising: a cylinder into which a washer fluid is supplied from a supply tank; a piston supported in the cylinder so as to move in an axial direction with a part of the piston projecting from the cylinder, the piston having a first flow path through which the washer fluid flows; a valve case having a plurality of jet nozzles from which the washer fluid is jetted and being connected to one end portion in the axial direction of the part of the piston projecting from the cylinder, the valve case having a second flow path connected to the first flow path, a plurality of third flow paths branching off the second flow path and communicating with the plurality of jet nozzles, respectively, and a branch portion at which the second flow path and the plurality of third flow paths are connected together; and a valve disposed in the branch portion and adapted to move in accordance with a fluid pressure of the washer fluid to open or close the branch portion so as to start or stop a supply of the washer fluid from the second flow path to the plurality of third flow paths, characterized in that the piston has a piston-side fitting portion at the one end portion in the axial direction, the piston-side fitting portion having an indented shape in which projecting portions and recess portions are aligned alternately in a circumferential direction, wherein the valve case has a case-side fitting portion for fitment with the piston-side fitting portion, the case-side fitting portion having an indented shape in which projecting portions and recess portions are aligned alternately in a circumferential direction, wherein the projecting portions and the recess portions of the case-side fitting portion are fitted in and on the recess portions and the projecting portions of the piston-side fitting portion so that the piston and the valve case are connected together, wherein the piston has a cylindrical portion which has a regular hexagonal cross section and the front end portion thereof is provided as the piston-side fitting portion, and wherein the piston-side fitting portion is formed so that the projecting portions (11a, 11a) are disposed one for each side of the regular hexagon in an alternating fashion. a cylinder into which a washer fluid is supplied from a supply tank; a piston supported in the cylinder so as to move in an axial direction with a part of the piston projecting from the cylinder, the piston having a first flow path through which the washer fluid flows; a valve case having a plurality of jet nozzles from which the washer fluid is jetted and being connected to one end portion in the axial direction of the part of the piston projecting from the cylinder, the valve case having a second flow path connected to the first flow path, a plurality of third flow paths branching off the second flow path and communicating with the plurality of jet nozzles, respectively, and a branch portion at which the second flow path and the plurality of third flow paths are connected together; and a valve disposed in the branch portion and adapted to move in accordance with a fluid pressure of the washer fluid to open or close the branch portion so as to start or stop a supply of the washer fluid from the second flow path to the plurality of third flow paths, characterized in that the piston has a piston-side fitting portion at the one end portion in the axial direction, the piston-side fitting portion having an indented shape in which projecting portions and recess portions are aligned alternately in a circumferential direction, wherein the valve case has a case-side fitting portion for fitment with the piston-side fitting portion, the case-side fitting portion having an indented shape in which projecting portions and recess portions are aligned alternately in a circumferential direction, wherein the projecting portions and the recess portions of the case-side fitting portion are fitted in and on the recess portions and the projecting portions of the piston-side fitting portion so that the piston and the valve case are connected together, wherein the piston has a cylindrical portion which has a regular hexagonal cross section and the front end portion thereof is provided as the piston-side fitting portion, and wherein the piston-side fitting portion is formed so that the projecting portions (11a, 11a) are disposed one for each side of the regular hexagon in an alternating fashion.