The victim – named locally as Richard Hellowell – was trapped under a machine, thought to be an earth-mover, for more than an hour.
His distraught mother rushed to the scene to be with him.
The horrific accident happened on a site at New Road, Luddenden, where new homes are being built.
Police, firefighters from Halifax and paramedics were called out just after 12.15pm on Friday.
The dead man is local and is believed to have worked for West End Joiners and Builders, of Farrar Mill, Rookery Lane, Salterhebble, Halifax.
A spokesman for the Health and Safety Executive, which investigates incidents in work places, confirmed it had launched an investigation.
Det Insp Tony Nicholson said: "It appears to have been a tragic accident and we are not treating the incident as suspicious. The man was working at the site when an accident occurred involving an earth-moving machine.
"The accident investigation branch attended, as did the Health and Safety Executive."