In newspaper articles and the publishing industry, there is an opinion that a decrease in the sale of books affects an increase in the lending of books in public libraries. However, there are few proof cases of the correlation and causality between these variables. We sought to empirically study whether the two variables truly demonstrate correlation or causality. We used data from 1970 to 2015. 　　The regression coefficient for the two variables of level data showed very high significance. However, this was a case of“ spurious regression.” The“ spurious regression” theory was proved by Granger and Newbold（ 1974）. We then performed regression analysis using stationary time series data, and the data after removing the time trend. We conducted a unit root test to derive the stationary time series data. Additionally, we used the Hodrick-Prescott filter to remove the time trend. Analysis of these data did not return a significant regression coefficient. We conclude that the lending of books at the public library has no effect on the sales of books.