A work vehicle comprising: an auxiliary machine fixing portion formed integrally with an engine section (Eu) and capable of attaching an engine auxiliary machine; an attachment device for attaching the engine auxiliary machine to the auxiliary machine fixing portion; a support table member included in the attachment device and configured to attach the engine auxiliary machine to the auxiliary machine fixing portion under a predetermined posture; a coupling mechanism included in the attachment device and configured to fixedly couple the support table member to the auxiliary machine fixing portion; a coupling bolt included in the coupling mechanism and provided to extend through the support table member and the auxiliary machine fixing portion; and an abutment member included in the coupling mechanism to come into abutment against the auxiliary machine fixing portion on the side oppose the side abutted by the support table member across the auxiliary machine fixing portion, the abutment member having a nut portion threaded to the coupling bolt; wherein in the abutment member, there is formed a locking protrusion protruding to the side where the auxiliary machine fixing portion is present as the target of abutment; wherein in the auxiliary machine fixing portion, there are formed an insertion hole for the coupling bolt and an anti-rotation hole in which the locking protrusion can be fitted; wherein the locking protrusion has its protrusion amount in the protruding direction set such that the locking protrusion is fitted in the anti-rotation hole between a state where the abutment member is at its maximally fastened position in abutment against the auxiliary machine fixing portion and a state where the abutment member is at a temporarily fastened position set to a loosening side by a predetermined amount from the maximally fastened state; and wherein the locking protrusion has the protrusion amount in the protruding direction set such that the locking protrusion is located at a position withdrawn from the anti-rotation hole when the abutment member is located at a position farther from the auxiliary machine fixing portion than the temporarily fastened position. an auxiliary machine fixing portion formed integrally with an engine section (Eu) and capable of attaching an engine auxiliary machine; an attachment device for attaching the engine auxiliary machine to the auxiliary machine fixing portion; a support table member included in the attachment device and configured to attach the engine auxiliary machine to the auxiliary machine fixing portion under a predetermined posture; a coupling mechanism included in the attachment device and configured to fixedly couple the support table member to the auxiliary machine fixing portion; a coupling bolt included in the coupling mechanism and provided to extend through the support table member and the auxiliary machine fixing portion; and an abutment member included in the coupling mechanism to come into abutment against the auxiliary machine fixing portion on the side oppose the side abutted by the support table member across the auxiliary machine fixing portion, the abutment member having a nut portion threaded to the coupling bolt; wherein in the abutment member, there is formed a locking protrusion protruding to the side where the auxiliary machine fixing portion is present as the target of abutment; wherein in the auxiliary machine fixing portion, there are formed an insertion hole for the coupling bolt and an anti-rotation hole in which the locking protrusion can be fitted; wherein the locking protrusion has its protrusion amount in the protruding direction set such that the locking protrusion is fitted in the anti-rotation hole between a state where the abutment member is at its maximally fastened position in abutment against the auxiliary machine fixing portion and a state where the abutment member is at a temporarily fastened position set to a loosening side by a predetermined amount from the maximally fastened state; and wherein the locking protrusion has the protrusion amount in the protruding direction set such that the locking protrusion is located at a position withdrawn from the anti-rotation hole when the abutment member is located at a position farther from the auxiliary machine fixing portion than the temporarily fastened position.