A gate valve 1 includes: a plate 2 having an opening portion 9; a plate 3 located opposite to the plate 2; a guide space 5 formed between the plates 2, 3; and a plate 6 provided in the space 5. The plate 6 is slidable along a direction in which an opening portion 11 is offset from the opening portion 9 in the space 5 in a state in which the plate 6 is pressed by the pressing portion 13 and separated from the plate 2, and a position of the plate 6 is fixed with respect to the plate 2 in the space 5 in a state in which the plate 6 is pressed by the pressing portion 16 and is in contact with the plate 2. The pressing portions 13, 16 each have a bellows structure formed by diffusion-bonding metal plates 18 and 19 to each other.