A fixing device for a support of a weaving machine, the fixing device comprising: a fastener comprising a head insertable into a support groove that is recessed in an inclined surface formed on a front portion of a sley of the weaving machine from a front opening of the support groove; a shank connected to the head and having a pair of projections, each of the projections extending outward in a radial direction of the shank; and an external-thread portion formed on the shank, wherein the shank protrudes out of the front opening with the head placed in the support groove, and the head is rotated around an axis of the shank with rotation of the shank so that the head is held in the support groove; and a nut mounted to the external-thread portion; wherein the shank is insertable through an insertion hole formed in the support so that each projection can contact a hole wall of the insertion hole to regulate a rotation of the fastener, wherein the head has an approximately quadrilateral shape that has a pair of long sides (61, 62, 71, 72) and a pair of short sides (63, 64, 73, 74), at least one of the short sides (63, 64, 73, 74) has a straight portion (66, 69, 76, 79), and a distance between one end of the at least one short side (63, 64, 73, 74) and the axis is longer than a distance between the other end of the at least one short side (63, 64, 73, 74) and the axis, and the straight portion (66, 69, 76, 79) intersects at a right angle an imaginary orthogonal line that passes through the axis. a fastener comprising a head insertable into a support groove that is recessed in an inclined surface formed on a front portion of a sley of the weaving machine from a front opening of the support groove; a shank connected to the head and having a pair of projections, each of the projections extending outward in a radial direction of the shank; and an external-thread portion formed on the shank, wherein a head insertable into a support groove that is recessed in an inclined surface formed on a front portion of a sley of the weaving machine from a front opening of the support groove; a shank connected to the head and having a pair of projections, each of the projections extending outward in a radial direction of the shank; and an external-thread portion formed on the shank, wherein the shank protrudes out of the front opening with the head placed in the support groove, and the head is rotated around an axis of the shank with rotation of the shank so that the head is held in the support groove; and a nut mounted to the external-thread portion; wherein the shank is insertable through an insertion hole formed in the support so that each projection can contact a hole wall of the insertion hole to regulate a rotation of the fastener, wherein the head has an approximately quadrilateral shape that has a pair of long sides (61, 62, 71, 72) and a pair of short sides (63, 64, 73, 74), at least one of the short sides (63, 64, 73, 74) has a straight portion (66, 69, 76, 79), and a distance between one end of the at least one short side (63, 64, 73, 74) and the axis is longer than a distance between the other end of the at least one short side (63, 64, 73, 74) and the axis, and the straight portion (66, 69, 76, 79) intersects at a right angle an imaginary orthogonal line that passes through the axis.