PURPOSE: To inspect a reactor pressure vessel for a ship reactor comprized by placing an integral reactor pressure vessel which is covered in one with a water-sealed vessel instaling insulator inside and submerged in water in a containment.

CONSTITUTION: In a reactor containment 4, a reactor pressure vessel 2 is contained in the state dipped in water in the containment with no contact. A neutron shield 11 covering the lower space of the reactor pressure vessel separates the contact of the reactor pressure vessel 2 and the containment water and insulation material 8 is installed inside. Therefore, there is no need of placing a water sealed vessel 7 around the reactor pressure vessel 2 in the region the neutron shield 11 is covering the reactor pressure vessel 2 and the space 13 is expanded so that by using the space 13, an inspection device can be put close to the outer surface of the vessel 2.