Truck frame for construction machine

A truck frame for a construction machine, said truck frame including left and right side frames and a center frame disposed between said side frames, comprising:

• said center frame being constituted by a top plate and a bottom plate which are connected to said left and right side frames at an interval in a vertical direction, a connecting tubular body provided between intermediate portions in left and right directions of said top plate and said bottom plate to connect said top plate and said bottom plate, and a cylindrical circle member which is secured to an upper surface side of said top plate and on an upper end side of which a swing circle is mounted,
• said circle member is formed such that its upper end side is formed as an upper thick-walled portion, its lower end side is formed as a lower thick-walled portion, each of said upper and lower thick-walled portions having a same plate thickness,
• an outer curved portion is provided in an outer peripheral surface of said circle member, said outer curved portion being located between said upper thick-walled portion and said lower thick-walled portion and formed by cutting out a recessed groove shape over an entire circumference,
• an inner curved portion is provided in an inner peripheral surface of said circle member, said inner curved portion being located between said upper thick-walled portion and said lower thick-walled portion and is formed by cutting out a recessed groove shape over an entire circumference, and
• a portion between said upper thick-walled portion and said lower thick-walled portion is formed as an hourglass-shaped thin-walled portion having a smaller plate thickness than the plate thickness of said upper and lower thick-walled portions and enclosed by said outer curved portion and said inner curved portion.