partition wall member 14 forming the air chamber b accordingly the width of partition wall member 14 can be enlarged to increase the capacity of air chamber b thereby to further reduce disorder in the injection amount of fuel although in the first embodiment all the three injection sockets 12 are aligned at the one sided position only the central injection socket 12 may be placed at the one sided position while the other injection sockets 12 may be placed at an appropriate position in the fuel delivery pipe the section of upper case 15 across the longitudinal direction is rounded at its whole corner and formed in a two stepped trapezoid with such configuration of the cross section of upper case 15 an inwardly curved portion 15 b 1 formed along the longitudinal direction of upper case 15 displaces in a direction of its thickness in accordance with fluctuation of fuel pressure in the internal space a to absorb pressure pulsations of fuel in the internal space a since the pressure pulsations of fuel in the internal space a are absorbed by displacement of the curved portion 15 b 1 in addition to suppression caused by fluctuation of the capacity of the air chamber b disorder in the injection amount of fuel is further reduced in a modification of the fuel delivery pipe the ceiling wall 15 b of upper case 15 may be flattened without curved portion 15 b 1 in such a modification the partition wall member 14 is brazed at its radial flange 14.