Global tourism has recently gained momentum alongside the expansion of the global economy. Japan is increasingly focusing on tourism as a valuable boost to its economy. This study investigates the trends of outbound tourists to gain insight into inbound tourism. We selected passport statistics as a novel data source for inclusion in our analytical model. Logarithmic multiple regression analysis was conducted using the number of Japanese nationals departing Japan and the number of newly issued general passports as the objective variables. We included the size of the working-age population and the exchange rate, or the working-age population and the productivity index, as parameters, respectively. In both cases, the logarithmic model displayed a good fit. We demonstrate the effectiveness of introducing a previously unexplored ‘passport’ factor into models when forecasting international tourist numbers.