Fuel injection valve and fuel injection device

A fuel injection device characterized in that it comprises a fluid path to which high-pressure fluid is supplied externally, a spray hole which connects with said fluid path and sprays at least a portion of the high-pressure fluid, a branch path which diverges from said fluid path and has a closed tip end, a diaphragm which connects with said branch path and has at least a portion which strains and deforms when subjected to pressure of said high-pressure fluid which is changed by spraying of the fluid from the spray hole, displacement sensing means for sensing a displacement of said diaphragm, an injector body which has said fluid path and said spray hole formed therein, and a separate member which is formed to be separate from said injector body and disposed inside said injector body is disclosed. Further, said separate member has formed therein a hole or a groove which communicates with said fluid path to form at least a portion of said branch path and a thin-walled portion which communicates with said hole or said groove to form said diaphragm.