A seed sowing machine, comprising: a groove opening mechanism forming a groove in soil while moving in a direction of travel, comprising: 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 said disk colter in relation to the direction of travel and widening the groove cut by said disk colter, wherein said 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 the disk colter side toward a rear; and wherein the widening section has a stiffening plate member in the disk colter side, and wherein the stiffening plate member overlaps a part of the outer circumference of the disk colter when viewed from a side surface in relation to the direction of travel; a seed guiding member which forms a slit and is provided adjacently in a rear of said widening section, wherein a seed is discharged from the slit; characterised by a slit cleaning mechanism including: a rotary shaft whose axial direction is a width direction of the slit; a reset lever fixed to the rotary shaft; a cleaning member one end of which is fixed to the reset lever and the other end of which extends to a ground surface side and is disposed inside the slit; and an elastic body one end of which is mounted on the reset lever and the other end of which is fixed to an opposite side of the reset lever in relation to said rotary shaft. 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 said disk colter in relation to the direction of travel and widening the groove cut by said disk colter, wherein said 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 the disk colter side toward a rear; and wherein the widening section has a stiffening plate member in the disk colter side, and wherein the stiffening plate member overlaps a part of the outer circumference of the disk colter when viewed from a side surface in relation to the direction of travel; a seed guiding member which forms a slit and is provided adjacently in a rear of said widening section, wherein a seed is discharged from the slit; characterised by a slit cleaning mechanism including: a rotary shaft whose axial direction is a width direction of the slit; a reset lever fixed to the rotary shaft; a cleaning member one end of which is fixed to the reset lever and the other end of which extends to a ground surface side and is disposed inside the slit; and an elastic body one end of which is mounted on the reset lever and the other end of which is fixed to an opposite side of the reset lever in relation to said rotary shaft. a rotary shaft whose axial direction is a width direction of the slit; a reset lever fixed to the rotary shaft; a cleaning member one end of which is fixed to the reset lever and the other end of which extends to a ground surface side and is disposed inside the slit; and an elastic body one end of which is mounted on the reset lever and the other end of which is fixed to an opposite side of the reset lever in relation to said rotary shaft.