PROBLEM TO BE SOLVED: To easily exchange an earth pressure gauge of a mud pressure shield machine.SOLUTION: An earth pressure gauge 11a of a mud pressure shield machine is provided in a seal housing 11bh communicating with a through-hole 7a formed in a barrier 7 at a freely movable state, and is structured to be exchangeable by being taken out to a machine interior side. When exchanging the earth pressure gauge 11a, a slurry forming material is injected as a replacement material into a space on the opposite side of the earth pressure gauge 11a through an injection pipe 11bt while retreating the earth pressure gauge 11a, thereby preventing mud in a chamber from intruding into the seal housing 11bh through the through-hole 7a. After the earth pressure gauge 11a is made to retreat more than a sluice valve 11bp at a middle position of the seal housing 11bh, the sluice valve 11bp is closed and then the earth pressure gauge 11a is taken out from the seal housing 11bh and is exchanged.
