To provide an assembling method for preventing a plate-like member from tilting in assembling the plate-like member having a hole to be fitted with an axis portion on an assembled body having the axis portion protruding upward.

The method for assembling an impeller 20 as a plate-like member on an armature 30 as an assembled body comprises: a step A of adsorbing and horizontally retaining the impeller 20 on the lower end face of an adsorption head 5; a step B of moving the adsorption head 5 down toward the armature 30, with a hole 23 of the impeller 20 is being aligned with an axis portion 31 of the armature 30; a step C of releasing the adsorption and retention of the impeller 20, preventing the impeller 20 from tilting by contacting an end face 73 on the upper surface 21 of the impeller 21 using a push-in sleeve 7 and guiding the impeller 20 so that the hole 23 follows the axis portion 31 to be fitted with the axis portion 31; and a step D of pushing the impeller 20 in the axis portion 31 of the armature 30 with the push-in sleeve 7 after the hole 23 is fitted with the end of the axis portion 31.