A three-side covering seam-type bellows includes a plurality of essentially C-shaped sheets of mutually identical configuration, the sheets being piled to each other for forming the bellows. The bellows has a pair of obliquely extending lower edges provided for each of the sheets. An outer sewing line extends along the outer peripheral edge of each of the sheets, the outer sewing line extending to the inner end of the obliquely extending lower edges, and an inner sewing line extends along the inner peripheral edge of each of the sheets, the inner sewing line being terminated at terminating points on the inner peripheral edges extending from the inner end of the obliquely extending edge and spaced apart from the inner end. A pair of unsewn portions are formed between the inner ends and the termination points.