The injection apparatus is provided with a high speed step cylinder, a pressure accumulation part and a coupling mechanism. The high speed step cylinder has a rod and an operating chamber. The coupling mechanism is capable of switching between a coupled state in which the movement of the rod is restricted, and a non-coupled state in which the coupled state is released so as to enable the rod to move due to the operating pressure. The coupling mechanism includes a first coupling member, a second coupling member and a drive source. The coupling mechanism is kept in the coupled state in which the second coupling member is rotated to less than 90°. When the second coupling member is forced to rotate in the coupled state, the first coupling member rotates such that a first contact surface is in contact with a second contact surface.