We measure the effect of incentive payments on residential time-of-day (TOD) electricity demand in summer, using data from a residential TOD electricity pricing experiment in the Kyushu region of southern Japan. During the experiment, participating households could receive incentive payments if they reduce their peak usage share. Results based on an econometric model indicate that households have shifted their electricity usage from peak to off-peak periods in response to the incentive payment, but the effect of the incentive payment on load shifting was modest.