In this paper, we investigate the effects of the Bank of Japan’s (BOJ) exchangetraded fund (ETF) purchase program on equity risk premia. We first construct a unique panel dataset for the amount of individual stock that the BOJ has indirectly purchased in the program. Then, utilizing the cross-sectional and time-series variations in purchases associated with the BOJ’s policy changes, the empirical analysis reveals that: (i) the BOJ’s ETF purchases instantaneously support stock prices on the days of purchases, and (ii) the instantaneous positive effects on stock prices, combined with the countercyclical nature of the BOJ’s purchases, have decreased the market beta and coskewness of Japanese stocks, thus leading to an economically significant decline in risk premia.