An internal combustion engine with a fuel injector comprising: an injector body in which a fuel flow path is formed which extends from a fuel inlet to a spray hole, said injector body being mounted in a cylinder head of the internal combustion engine; an actuator disposed within said injector body, said actuator working to open the spray hole to spray fuel, as supplied to the fuel flow path through the fuel inlet, to the internal combustion engine; and a fuel pressure sensor working to measure a pressure of the fuel in said injector body and produce an electric signal indicative thereof, wherein said fuel pressure sensor is installed in a first portion of said injector body which is located outside a mount hole formed in the cylinder head and which is located away from the cylinder head of the internal combustion engine and away from a second portion of said injector body on which a mechanical pressure is exerted by an external member, characterized in that said external member is a clamp placed in abutment with a surface of said injector body to exert pressure on said injector body to mount said injector body in the mount hole formed in the cylinder head, wherein the surface of said injector body is the second portion of said injector body on which the mechanical pressure that is the pressure exerted by the clamp acts, and the fuel pressure sensor is equipped with a stem working as a pressure deformable member which is sensitive to the pressure of fuel in the fuel flow path to deform elastically and a strain gauge working to convert the elastic deformation or distortion of the stem into said electric signal. an injector body in which a fuel flow path is formed which extends from a fuel inlet to a spray hole, said injector body being mounted in a cylinder head of the internal combustion engine; an actuator disposed within said injector body, said actuator working to open the spray hole to spray fuel, as supplied to the fuel flow path through the fuel inlet, to the internal combustion engine; and a fuel pressure sensor working to measure a pressure of the fuel in said injector body and produce an electric signal indicative thereof, wherein said fuel pressure sensor is installed in a first portion of said injector body which is located outside a mount hole formed in the cylinder head and which is located away from the cylinder head of the internal combustion engine and away from a second portion of said injector body on which a mechanical pressure is exerted by an external member, characterized in that said external member is a clamp placed in abutment with a surface of said injector body to exert pressure on said injector body to mount said injector body in the mount hole formed in the cylinder head, wherein the surface of said injector body is the second portion of said injector body on which the mechanical pressure that is the pressure exerted by the clamp acts, and the fuel pressure sensor is equipped with a stem working as a pressure deformable member which is sensitive to the pressure of fuel in the fuel flow path to deform elastically and a strain gauge working to convert the elastic deformation or distortion of the stem into said electric signal.