Swivel frame

A swivel frame for a swivel work machine includes a swivel base plate (57) supported on a traveling machine body (3) to be pivotable about a swivel axis (X) and mounting an engine (35) at a rear portion thereof, a support bracket (17) provided at a front end of the swivel base plate (57) for supporting an excavator (6), a partition wall (59) provided on the swivel base plate (57) for partitioning space forwardly of the engine (35) in the fore/aft direction, and a pair of right and left vertical ribs (61R,61L) provided on the swivel base plate (57) for interconnecting the support bracket (17) and the partition wall (59). The swivel base plate (57) is divided into a rear plate portion (66) on the rear side thereof and a front plate portion (67) on the front side thereof, the rear plate portion (66) being formed of a plate thinner than the front plate portion (67). The rear plate portion (66) and the front plate portion (67) are fixedly connected to each other in such a manner that upper surfaces thereof are flush each other. A rear portion of the front plate portion (67) projects more rearward than the partition wall (59). A pair of vertical walls (69L,69R) are formed on and project from the rear plate portion (66). Front portions (69LF,69RF) of the pair of vertical walls (69L,69R) project more forward than the rear plate portion (66) and are fixedly attached to the rear portion of the front plate portion (67) and the partition wall (59).