[Claim 1] A fuel injection valve, comprising:
a core having a cylindrical shape;
a valve seat, which has a seat surface formed therein, and is arranged on a downstream side of flow of fuel with respect to the core;
a valve body, which is arranged between the core and the seat surface so as to be displaceable, and is configured to close a fuel passage when the valve body is brought into contact with the seat surface and open the fuel passage when the valve body is separated away from the seat surface;
a holder having a cylindrical shape, which is configured to accommodate the valve seat and the valve body;
a spring configured to urge the valve body in such a direction that the valve body is brought into contact with the seat surface; and
a coil configured to generate an electromagnetic attraction force of displacing the valve body against an urging force of the spring in such a direction that the valve body is separated away from the seat surface,
wherein the valve body includes:
an armature, which has a cylindrical shape, and is opposed to the core; and
a valve-body main body fixed to the armature,
wherein the valve-body main body is brought into contact with

the seat surface through displacement of the armature in such a direction that the armature is separated away from the core, and the valve-body main body is separated away from the seat surface through displacement of the armature in such a direction that the armature approaches the core,
wherein an end portion of the armature on the core side includes:
a convex portion; and
a flat-surface forming portion located on a radially outer side with respect to the convex portion,
wherein the flat-surface forming portion includes a first orthogonal flat-surface portion continuous from the convex portion,
wherein the first orthogonal flat-surface portion is parallel to a plane orthogonal to an axial line of the armature,
wherein the convex portion protrudes toward the core with respect to a position of the first orthogonal flat-surface portion, and
wherein, in a plane including the axial line of the armature, an outline of the convex portion is a curved line having an arc shape, which is continuous from an inner peripheral surface of the armature.
[Claim 2] The fuel injection valve according to claim 1, wherein the convex portion is arranged in an annular shape along a circumferential direction of the armature.

[Claim 3] The fuel injection valve according to claim 2, wherein the convex portion has a concave portion.
[Claim 4] The fuel injection valve according to claim 1,
wherein the end portion of the armature on the core side
includes a plurality of the convex portions, and
wherein the plurality of convex portions are arranged at
intervals in a circumferential direction of the armature.
[Claim 5] The fuel injection valve according to claim 4, wherein an outer surface of each of the plurality of convex portions has a shape of a portion of a spherical surface.
[Claim 6] The fuel injection valve according to any one of claims 1 to 5,
wherein the flat-surface forming portion includes a second orthogonal flat-surface portion located on the radially outer side with respect to the first orthogonal flat-surface portion,
wherein the second orthogonal flat-surface portion is parallel to the plane orthogonal to the axial line of the armature, and
wherein a distance between the second orthogonal flat-surface portion and the core is larger than a distance between the first orthogonal flat-surface portion and the core.

[Claim 7] The fuel injection valve according to claim 6, wherein a curved surface portion is formed between the first orthogonal flat-surface portion and the second orthogonal flat-surface portion so as to smoothly connect the first orthogonal flat-surface portion and the second orthogonal flat-surface portion to each other.
[Claim 8] The fuel injection valve according to any one of claims 1 to 7, wherein the end portion of the armature on the core side includes an armature-side tapered surface portion that is inclined in a direction of being separated away from the core from the flat-surface forming portion toward the radially outer side.
[Claim 9] The fuel injection valve according to claim 8, wherein a curved surface portion is formed between the flat-surface forming portion and the armature-side tapered surface portion so as to smoothly connect the flat-surface forming portion and the armature-side tapered surface portion to each other.
[Claim 10] The fuel injection valve according to any one of claims 1 to 9,
wherein an end portion of the core on the armature side includes a core-side tapered surface portion that is inclined in a direction of being separated away from the armature toward a radially inner side of the core, and

wherein the convex portion is opposed to the core-side tapered surface portion.
[Claim 11] The fuel injection valve according to any one of claims 1 to 10, wherein a curved surface portion is formed between the convex portion and the first orthogonal flat-surface portion so as to smoothly connect the convex portion and the first orthogonal flat-surface portion to each other.