To provide an X-ray diagnostic system allowing easy acquisition of a jaw deformity decision index, an obstructive sleep apnea syndrome risk decision index or the like, and allowing easy and short-time jaw deformity decision, obstructive sleep apnea syndrome risk decision or the like by use of the indexes.

An X-ray diagnostic system includes: a photographing apparatus (1, 20) performing the head and neck X-ray photography of a subject; and a data processor (10) calculating P by a prescribed expression by use of a distance selected from the group consisting of a distance (S (Sella)-A) between S and A, a distance (S-N (Nasion)) between S and N, a distance (S-X_i) between S and X_i (i is an integer ≥1 and ≤4, X₁=B, X₂=Pog (Pogonion), X₃=Gn (Gnathion), and X₄=Me (menton)), a distance (Go (Gonion)-X_j) between Go and Xj (j is an integer ≥1 and ≤4, j=i or j≠i), a distance (Go-A) between Go and A, and a distance (Cd (condylion)-Go) between Cd and Go, which are measured by the head and neck X-ray photography.