Police said the accident happened at about 11am at the cross in front of Wat Nong Saeng in Moo 8 village in Tambon Ban Song.
The pickup flipped over in the crash.
The driver was Samak Poon-udom, with passengers Rungrit Kansuwan, Kimsuang Kansuwann, and Yanisa Poon-udom.
Police learned from their relatives that the four, who were relatives, were coming from Chumphon to visit relatives in Wieng Sa.
The driver apparently did not see the incoming Chumphon-Hat Yai train as he was not familiar with the road so he cut the front of the train, police said. The rail crossing does not have a barricade.
No one on the train was injured and the train did not derail, so it proceeded to its destination shortly after the accident.