A fuel cell stack assembly device is provided. The assembly device includes a stack guide apparatus that arranges and stacks fuel cells using a plurality of guide bars and a press unit that repeatedly moves vertically based on the stack guide apparatus and presses the fuel cells stacked on the stack guide apparatus. A roller structure includes a roller in rolling contact with the guide bar and is installed at the press unit. A weight detection portion detects weight that is applied to the roller by the guide bar. Additionally, a controller determines whether the guide bar is at the home position based on a detection signal of the weight detection portion and operates the press unit.