A camshaft drive device comprising: a cam sprocket, which is attached to a camshaft; a chain, which is wound around the cam sprocket; a guide lever, which guides the chain and has a support hole; and a chain chamber, which is provided in a cylinder head to accommodate the chain and the guide lever, the chain chamber being defined by a front wall and a rear wall facing each other in an axial direction, characterized by comprising: a support bolt, which pivotably supports the guide lever, the support bolt including a head portion that is formed in a front end portion, a male screw portion that is formed in a rear end portion, and a shaft portion that is formed between the head portion and the male screw portion and is pivotably and slidably inserted through the support hole of the guide lever; an insertion hole, which is provided in the front wall and through which the support bolt is inserted from a front side; and a female screw hole, which is provided in the rear wall and into which the male screw portion of the support bolt is screwed, wherein a length from a rear end to a front end of the shaft portion is longer than an axial distance from a front end of the support hole to a front end of the insertion hole in a state where the guide lever abuts on the rear wall. a cam sprocket, which is attached to a camshaft; a chain, which is wound around the cam sprocket; a guide lever, which guides the chain and has a support hole; and a chain chamber, which is provided in a cylinder head to accommodate the chain and the guide lever, the chain chamber being defined by a front wall and a rear wall facing each other in an axial direction, characterized by comprising: a support bolt, which pivotably supports the guide lever, the support bolt including a head portion that is formed in a front end portion, a male screw portion that is formed in a rear end portion, and a shaft portion that is formed between the head portion and the male screw portion and is pivotably and slidably inserted through the support hole of the guide lever; an insertion hole, which is provided in the front wall and through which the support bolt is inserted from a front side; and a female screw hole, which is provided in the rear wall and into which the male screw portion of the support bolt is screwed, wherein a length from a rear end to a front end of the shaft portion is longer than an axial distance from a front end of the support hole to a front end of the insertion hole in a state where the guide lever abuts on the rear wall. a support bolt, which pivotably supports the guide lever, the support bolt including a head portion that is formed in a front end portion, a male screw portion that is formed in a rear end portion, and a shaft portion that is formed between the head portion and the male screw portion and is pivotably and slidably inserted through the support hole of the guide lever; an insertion hole, which is provided in the front wall and through which the support bolt is inserted from a front side; and a female screw hole, which is provided in the rear wall and into which the male screw portion of the support bolt is screwed, wherein a length from a rear end to a front end of the shaft portion is longer than an axial distance from a front end of the support hole to a front end of the insertion hole in a state where the guide lever abuts on the rear wall.