Patent ID: 7168302

Claim:
A diagnostic device of an evaporated fuel processing system for closing the evaporated fuel processing system including a fuel tank and then executing a leak diagnosis of the evaporated fuel processing system after changing an internal pressure thereof from a criterion pressure value to a target pressure value, comprising: an internal pressure detection section for detecting an internal pressure value of the evaporated fuel processing system; and a diagnostic section for executing the leak diagnosis based on a change amount between the respective internal pressure values at a start timing and at a termination timing to calculate a pressure change therebetween, wherein said start timing is set on the basis of a timing when the internal pressure value detected by said internal pressure detection section reaches a peak pressure value, which is different from said target pressure value and occurs after the internal pressure value reaches the target pressure value and the evaporated fuel processing system is closed, and said termination timing is set at a later timing than the start timing.