An artificial hip joint stem, comprising: a concave part located in a shoulder part of a stem body, the concave part comprising an opening part that opens into the shoulder part, and a wall part extending along a stem central axis of the stem body, the wall part comprising an inner wall portion and an outer wall portion opposed to each other, and a front wall portion and a rear wall portion opposed to each other, wherein a distance between the inner wall portion and the outer wall portion decreases going toward a distal end of the concave part from the opening part in a sectional view that is parallel to the stem central axis and includes the inner wall portion and the outer wall portion, and both the front wall portion and the rear wall portion have a planar region in a sectional view that is parallel to the stem central axis and includes the front wall portion and the rear wall portion, characterised in that the concave part further comprises a chamfered portion formed by chamfering an edge portion of the wall part over an entire circumference of the opening part. a concave part located in a shoulder part of a stem body, the concave part comprising an opening part that opens into the shoulder part, and a wall part extending along a stem central axis of the stem body, the wall part comprising an inner wall portion and an outer wall portion opposed to each other, and a front wall portion and a rear wall portion opposed to each other, wherein a distance between the inner wall portion and the outer wall portion decreases going toward a distal end of the concave part from the opening part in a sectional view that is parallel to the stem central axis and includes the inner wall portion and the outer wall portion, and both the front wall portion and the rear wall portion have a planar region in a sectional view that is parallel to the stem central axis and includes the front wall portion and the rear wall portion, characterised in that the concave part further comprises a chamfered portion formed by chamfering an edge portion of the wall part over an entire circumference of the opening part. an opening part that opens into the shoulder part, and a wall part extending along a stem central axis of the stem body, the wall part comprising an inner wall portion and an outer wall portion opposed to each other, and a front wall portion and a rear wall portion opposed to each other, wherein a distance between the inner wall portion and the outer wall portion decreases going toward a distal end of the concave part from the opening part in a sectional view that is parallel to the stem central axis and includes the inner wall portion and the outer wall portion, and both the front wall portion and the rear wall portion have a planar region in a sectional view that is parallel to the stem central axis and includes the front wall portion and the rear wall portion, characterised in that an inner wall portion and an outer wall portion opposed to each other, and a front wall portion and a rear wall portion opposed to each other, wherein a distance between the inner wall portion and the outer wall portion decreases going toward a distal end of the concave part from the opening part in a sectional view that is parallel to the stem central axis and includes the inner wall portion and the outer wall portion, and both the front wall portion and the rear wall portion have a planar region in a sectional view that is parallel to the stem central axis and includes the front wall portion and the rear wall portion, characterised in that the concave part further comprises a chamfered portion formed by chamfering an edge portion of the wall part over an entire circumference of the opening part.