We investigate when voters favour social investment. Welfare states have transformed their core policies as a result of low economic growth and fiscal pressures. The social investment strategy, such as broader education provision and promotion of women's employment, aims at shifting the economy from the traditional Keynesian welfare state to the high-productivity economy by encouraging long-term and inclusive human capital formation. Social investment is popular among citizens in many developed economies, especially in the EU where governments promote social investment as part of their welfare policy packages. However, in Japan, the term ‘social investment’ is rarely used in policy discussions. Consequently, we ask what levels of voter support social investment policies have in such an environment; which voter characteristics are associated with social investment support; and whether voter support for social investment differs when placed in a broader policy context. To answer these questions, we conducted an online survey with a conjoint experiment. Our data analysis shows that social investment policies are popular among Japanese people, despite a lack of familiarity with the concept of social investment. We find that social libertarians and female respondents are more likely than social authoritarians and male respondents to support social investment. In addition, there is some evidence that higher income voters are favourable to social investment policies. Furthermore, voter support for social investment depends on the policy context. Support becomes weaker when social investment policies are presented in combination with decreasing levels of social security spending. Our results highlight what kinds of social investment policies could be achieved without damaging electoral fortunes.