An evaporated fuel processing device includes a relationship learning unit that, during a learning operation, learns the relationship between a valve opening start amount and a pressure difference. In particular, the relationship learning unit learns this relationship when a valve opening detection unit detects a plurality of different valve opening start amounts and a pressure difference detection unit detects a plurality of different pressure differences. Then, the relationship learning unit creates a relationship map between the valve opening start amount and the pressure difference. The evaporated fuel processing device then corrects the valve opening start amount based on this relationship map.