A thread cutter for a sewing machine includes a first thread seizing assembly reciprocally movable and seizing a needle thread having passed a bobbin case and a bobbin thread by a first thread seizing portion, a cutting blade located nearer to the needle hole side than a movement locus of the first assembly, and a second thread seizing assembly seizing both threads having been seized by the first assembly during backward movement of reciprocation of the first assembly, cutting both threads in cooperation with the cutting blade. When moved backward in the reciprocation, the first assembly is swung so that the first thread seizing portion comes close to the second thread seizing assembly. The second assembly has a distal end on which a second thread seizing portion is located. The second thread seizing portion is two-forked so that the cutting blade is interposed between the two-forked portions.