[Object] There are provided a groove opening mechanism capable of forming a groove at a high speed when the groove is to be formed in the ground such as a no-tillage field, without damaging a machine body by being tangled with a residue of a former crop, a weed, earth, or the like, and without hampering smooth rotation of a rotating portion, and a seed sowing machine having that groove opening mechanism. [Organization] A groove opening mechanism forming a groove in soil while moving in a direction of travel has: one disk colter rotating at a time of moving and making a cut in a vertical direction in relation to a ground surface with a blade edge provided in an outer circumference； and a widening section provided in a rear of the disk colter in relation to the direction of travel and widening the groove cut by the disk colter, wherein the widening section has, in a front surface of a disk colter side, a widening member in which a taper is formed in a direction widening from a disk colter side toward a rear.
