In a die clamping apparatus for an injection molding machine or the like, die clamping means for coupling and pressing a moving die plate 9 to a fixed die plate via a tie bar 15 has a die clamping cylinder consisting of two stages of a large-diameter cylinder 11 and a small-diameter cylinder 31 and a ram formed into two stages of a large-diameter ram 13 and a small-diameter ram 25. The large-diameter ram 13 is inserted in the large-diameter cylinder 11, and the small-diameter ram 25 is inserted in the small-diameter cylinder 31. The proximal end portion of the tie bar 15 is connected directly to the small-diameter ram 25. Large oil chambers 11c and 11d are provided on both sides of the large-diameter ram 13, and a small oil chamber 11e is provided on the tie bar connection side of the small-diameter ram 25. An oil pressure is supplied appropriately to each of the large oil chambers and the small oil chamber in the die clamping cylinder to appropriately move the tie bar 15. The apparatus constructed as described above can be manufactured at a low cost, and useless time for eliminating a gap between a ring grooves in the tie bar and an engagement teeth of half nuts caused by the adjustment to die thickness can be reduced.