To provide an assembling method for a spherical tank, for which inner scaffolding is not necessary.

In this tank, after forming an equator part 3 by assembling equator part split pieces 3a and temporarily assembling upper hemispheric part slit pieces 4 on the equator part 3, a moving truck 12 equipped with a working floor 12a which is freely ascendable and descendable and freely laterally movable, is positioned on the lower part of the temporarily assembled equator part 3, and welding and weld zone inspection are performed using the working floor 12a. After that by temporarily assembling lower hemispheric part slit pieces on the ground, by welding them and by inspecting the weld zones, the lower hemispheric part is completed. The lower hemispheric part is moved to an upper part, is assembled to the equator part 3, and is welded.