A cab capable of easily securing rollover protection strength at low manufacturing cost is offered. Four pillars are mounted in the front and rear, and left and right of the cab. Two of them are mounted respectively in a first position at the outer side portion where it bulges outward and in a second position on the inner side portion and opposite the first position in the left-and-right direction. At least one of the pillars is formed with a pipe. A U-shaped frame is firmly mounted between the upper ends of the left and right rear pillars among the four pillars, and directed rearward to form a U-shaped rear roof frame.