To easily assemble a load carrying platform, even if the mechanics are not highly skilled, and shorten the lead time.

A front end beam 10 and a cross member 11 are weldedly connected to a main frame 9 to fabricate a main frame assembled body 4. A cross member 5, a side rail 6, an erected front assembled body 7, and a rear member 8 are installed in the main frame assembled body 4 by means of bolt-connection, thereby fabricating a platform frame 2. Respective unit floor plates 3a constituting of a floor plate 3 are adhered (fixed) to the platform frame 2.