Gardaí were notified of the incident on Athlone Road on Tuesday at around 2.15pm.
Four other men were injured as a result of the collapse.
Three people - including the man who died - were taken to the Mullingar's regional hospital. One of the men was described by a gardaí spokesperson as being in "a critical condition."
Two others were taken to the Tullamore General Hospital.
The scene of the incident has been preserved. The Health and Safety Authority are investigating.
There are no further details.