An image processing apparatus for performing tomosynthesis, the apparatus comprising: obtaining means (104, 105) for obtaining projection images of a subject which is captured while changing a geometric arrangement which is a positional relationship, between a radiation source for irradiating a two-dimensional area of a two-dimensional detector and the two-dimensional detector; reconstruction means for reconstructing a tomogram, by performing filter processing based on first weights on the obtained projection images using a reconstruction filter and performing back projection processing based on second weights on filtered projection images, wherein angles, which correspond to each projection image obtained by each irradiation by the radiation source and are formed by a normal line (y-axis) perpendicular to a detection plane of the two-dimensional detector and a reference axis (ŷ-axis) of the radiation source, are different from each other, wherein the first weights and the second weights are set by a function based on a first angle (β) and a second angle (β t) as variables, the first angle (β) is an angle formed by a first line connecting a focal point of the radiation source to an isocenter of a plane (xz-plane) parallel to a detection plane of the two-dimensional detector and the normal line (y-axis) perpendicular to the detection plane of the two-dimensional detector, a second line connects the focal point of the radiation source to a pixel position on the two-dimensional detector, a third line connects the focal point of the radiation source to an intersection point (B: 0,0, zt) where a perpendicular line extending from a first point (A: xt,0,zt) where the second line intersects the detection plane of the two-dimensional detector intersects an axis (z-axis) perpendicular to the first line and the normal line (y-axis); a perpendicular line extending from the focal point intersects the detection plane of the two-dimensional detector at a second point on the detection plane, a third point is obtained by shifting the second point along the detection plane based on position information in a direction of the axis (z-axis) of the intersection point (B: 0,0, zt), a fourth line connects the third point to the focal point, the second angle (β t) is an angle formed by the third line and the fourth line, and each of the first weights is a cosine value of a third angle formed by the second line and the third line. obtaining means (104, 105) for obtaining projection images of a subject which is captured while changing a geometric arrangement which is a positional relationship, between a radiation source for irradiating a two-dimensional area of a two-dimensional detector and the two-dimensional detector; reconstruction means for reconstructing a tomogram, by performing filter processing based on first weights on the obtained projection images using a reconstruction filter and performing back projection processing based on second weights on filtered projection images, wherein angles, which correspond to each projection image obtained by each irradiation by the radiation source and are formed by a normal line (y-axis) perpendicular to a detection plane of the two-dimensional detector and a reference axis (ŷ-axis) of the radiation source, are different from each other, wherein the first weights and the second weights are set by a function based on a first angle (β) and a second angle (β t) as variables, the first angle (β) is an angle formed by a first line connecting a focal point of the radiation source to an isocenter of a plane (xz-plane) parallel to a detection plane of the two-dimensional detector and the normal line (y-axis) perpendicular to the detection plane of the two-dimensional detector, a second line connects the focal point of the radiation source to a pixel position on the two-dimensional detector, a third line connects the focal point of the radiation source to an intersection point (B: 0,0, zt) where a perpendicular line extending from a first point (A: xt,0,zt) where the second line intersects the detection plane of the two-dimensional detector intersects an axis (z-axis) perpendicular to the first line and the normal line (y-axis); a perpendicular line extending from the focal point intersects the detection plane of the two-dimensional detector at a second point on the detection plane, a third point is obtained by shifting the second point along the detection plane based on position information in a direction of the axis (z-axis) of the intersection point (B: 0,0, zt), a fourth line connects the third point to the focal point, the second angle (β t) is an angle formed by the third line and the fourth line, and each of the first weights is a cosine value of a third angle formed by the second line and the third line.