The accident in Hokkaido on Friday killed Chung Lung, 65, a high-ranking official in Taiwan’s Ministry of Culture, her 23-year-old son and 37-year-old daughter-in-law.
Chung’s 35-year-old son, whose wife was killed, was at the wheel and survived but was in a critical condition, said a police spokesman, adding roads had been slippery.
The Hokkaido Shimbun newspaper said the accident, on a sharp bend, appeared to have happened when the rental car veered into the path of the oncoming truck, whose driver escaped with a slight injury.
Hokkaido is the northernmost Japanese island and is popular with tourists from Asia, who visit for its unspoilt beauty, ski resorts, and seafood.