The blade apparatus includes a connection blade portion which is provided at its lower end with a central blade portion including a straight first cutting edge and having a second cutting edge which extends continuously with the first cutting edge through a predetermined angle rearwardly, and an end blade portion having a third cutting edge which extends continuously with a second cutting edge through a predetermined angle forwardly, wherein front surfaces of the blade portions are concave curved surfaces which are continuous from the upper end to the lower end, across line between the connection blade portion and the end blade portion and a cross point between the second cutting edge and the third cutting edge are located rearward of the cross point of the first cutting edge and the cross line between the central blade portion and the connection blade portion, and at least a central main region of the central blade portion is made of steel plate, and at least the connection blade portion and the end blade portion are integrally cast together with a back surface support portion and first and second brackets thereof.