A fuel injection control device of a diesel engine, the device comprising: a fuel injection valve which injects a fuel into a combustion chamber; and a fuel injection timing control unit which controls a fuel injection timing of the fuel from the fuel injection valve, wherein the fuel injection control device comprises: a standard fuel injection timing setting unit which previously sets a standard fuel injection timing with respect to engine speed and fuel injection quantity under a condition of normal atmospheric pressure and normal temperature; a penetration judging unit which judges whether or not the penetration of the fuel atomization burned in a cylinder is in an increasing condition, by use of a difference between an estimated ignition delay from an injection start timing to a combustion start timing and a standard ignition delay; and a fuel injection timing correction unit which, by correcting the fuel injection timing toward an advanced timing angle, constrains the penetration of the fuel atomization in a case where the penetration judging unit judges that the penetration of the fuel atomization is in an increasing condition, characterized in that the estimated level for the ignition delay from the injection start timing is computed based on the pressure and temperature inside of the intake manifold, and the oxygen concentration of inhaled gas; and it is judged that the penetration of the fuel atomization in the cylinder is in an increasing condition, in a case where the computed estimated ignition delay is greater than the standard ignition delay at an injection start timing according to the standard injection timing. a fuel injection valve which injects a fuel into a combustion chamber; and a fuel injection timing control unit which controls a fuel injection timing of the fuel from the fuel injection valve, wherein the fuel injection control device comprises: a standard fuel injection timing setting unit which previously sets a standard fuel injection timing with respect to engine speed and fuel injection quantity under a condition of normal atmospheric pressure and normal temperature; a penetration judging unit which judges whether or not the penetration of the fuel atomization burned in a cylinder is in an increasing condition, by use of a difference between an estimated ignition delay from an injection start timing to a combustion start timing and a standard ignition delay; and a fuel injection timing correction unit which, by correcting the fuel injection timing toward an advanced timing angle, constrains the penetration of the fuel atomization in a case where the penetration judging unit judges that the penetration of the fuel atomization is in an increasing condition, characterized in that the estimated level for the ignition delay from the injection start timing is computed based on the pressure and temperature inside of the intake manifold, and the oxygen concentration of inhaled gas; and it is judged that the penetration of the fuel atomization in the cylinder is in an increasing condition, in a case where the computed estimated ignition delay is greater than the standard ignition delay at an injection start timing according to the standard injection timing. a standard fuel injection timing setting unit which previously sets a standard fuel injection timing with respect to engine speed and fuel injection quantity under a condition of normal atmospheric pressure and normal temperature; a penetration judging unit which judges whether or not the penetration of the fuel atomization burned in a cylinder is in an increasing condition, by use of a difference between an estimated ignition delay from an injection start timing to a combustion start timing and a standard ignition delay; and a fuel injection timing correction unit which, by correcting the fuel injection timing toward an advanced timing angle, constrains the penetration of the fuel atomization in a case where the penetration judging unit judges that the penetration of the fuel atomization is in an increasing condition, characterized in that the estimated level for the ignition delay from the injection start timing is computed based on the pressure and temperature inside of the intake manifold, and the oxygen concentration of inhaled gas; and it is judged that the penetration of the fuel atomization in the cylinder is in an increasing condition, in a case where the computed estimated ignition delay is greater than the standard ignition delay at an injection start timing according to the standard injection timing.