There is provided a frame structure for a saddle-ridden type vehicle. A pair of tank rails are jointed to a head frame and extend rearward of a vehicle body from the head frame. The head frame includes a head pipe portion and a pair of arm portions being continuous with the head pipe portion and extending rearward of the vehicle body. Each of upper surfaces of at least one of rear end portions of the arm portions and front end portions of the tank rails are formed into a convex surface having an arc-shaped cross section. The rear end portions of the arm portions and the front end portions of the tank rails are respectively welded to each other so that end portions of weld beads are positioned at side surfaces thereof.