Reducing out-of-pocket costs is known to improve mammography attendance, but an evidence gap remains concerning Pap smear testing. The Japanese government implemented a politically determined intervention to remove out-of-pocket costs for Pap smear tests and mammography attendance, costing US$148 million, in 2009. It targeted women when they reached the first year of a 5-year age group (i.e., 20, 25, 30 years) with the aim of reducing attendance inequality. Our objective is to evaluate the intervention in terms of uptake and average cost per uptake for cancer screening attendance and to assess socioeconomic inequalities in cancer screening attendance pre- and postintervention. A quasi-experimental study utilizing national repeated cross sections, observed pre- and postintervention, which compared intervention and comparison groups by the Difference-in-Differences method, was conducted. Outcome measures were uptake of cancer screening attendance resulting from the intervention with average cost per uptake and broad inequality indicators for cancer screening attendance according to socioeconomic inequality. In total, 34,043 age-eligible, noninstitutionalized women were analyzed. Uptake among the overall population was 13.9% point in the age- and income-adjusted model for Pap smear and 9.8% point for mammography, with an average cost of US$139 per uptake. The intervention increased inequality indicators in Pap smear attendance (more than +100%) but decreased inequality in mammography attendance (ranging from -12.9 to -74.1%) within the intervention group. In conclusion, removing out-of-pocket costs improves female cancer screening uptake in Japan but may not be cost-saving. Although cost removal reduces inequalities in attendance for mammography, it appears to increase inequalities in Pap smear attendance.