[en] The construction of Materials and Life science experimental Facility (MLF) in J-PARC (Japan Proton Accelerator Complex) project has been completed. Since 2003, the detailed design, fabrication and examination for the mercury target vessel as pulsed neutron source were carried out by the vender. The mercury target vessel consists of the mercury vessel and the safety hull, which corves the mercury vessel, to prevent the leak of mercury to outside at the failure of the mercury vessel. The safety hull is a double-walled structure to make the cooling channel of heavy water to remove the heat due to the injection of the pulsed proton beams. Mercury and heavy water circulate in the mercury vessel and the safety hull, respectively. The helium gas in a space between the mercury vessel and the safety hull can prevent the inflow of mercury into heavy water at the failure of the mercury vessel. The design pressure of each medium is 0.5 MPaG. The temperature of the mercury target vessel and mercury rises at a moment of the proton beam injection and then the thermal shock and the deformation of the mercury vessel occur. The mercury target vessel is imposed by not only static load due to the inner pressure and dead weight but also repeated dynamic load. Based on loading conditions, the structural integrity of the mercury target vessel was evaluated using numerical analyses. The results were described as following. 1. It was confirmed that the mercury target vessel satisfied the criteria of JIS B 8266 in the case of all loading conditions. The deformation of the mercury vessel applied static load is less than 1 mm. 2. The natural frequency was larger than 50 Hz, which is sufficiently larger than 25 Hz of the frequency of proton beam injection. 3. The maximum repeated stress in the mercury target vessel at the proton beam injection was less than the stress (167 MPa) of the fatigue endurance curves in JIS B 8266. There was hardly possibility that the fatigue failure of the mercury vessel occurred due to the proton beam injection. (author)