Objective:This study examines whether hereditary constitutional monarchs have any influence on democratic public opinion, focusing on the case of the Japanese emperor. Methods: A survey experiment on the regulation of public expression. This issue can be framed both as left wing (i.e., the regulation of hate speech) and right wing (i.e., the regulation of publicly funded anti-nationalistic exhibitions). Taking advantage of the dual nature of the issue, we test the effects of the emperor's endorsement on support for regulation under each ideological frame. Results: The (former) emperor's endorsement for freedom of expression does have a cross-cutting effect and decreases support for regulation. This effect is relatively small but statistically significant. Additionally, the findings provide weak evidence for the emperor's own ideological position conditioning his endorsement effect. Conclusion: Hereditary monarchs do influence democratic public opinion, and their influence can cross-cut ideology. KEYWORDS constitutional monarch, emperor, endorsement, freedom of expression, Japan, public opinion, survey experiment Some present-day advanced democracies assign a strictly nonpolitical role to a certain powerful ruler such as monarch, that is, a hereditary head of state. Such political systems are called constitutional monarchies; some typical examples of these include the United Kingdom, Sweden, and Japan. In constitutional monarchies, although monarchs "often have constitutional prerogatives that are similar to those of powerful presidents, such as the power of governmental dismissal, their constitutional status ensures that they are in no position to use these powers" (Schleiter and Morgan-Jones 2009:499). 1 Forbidden to 1 Constitutional monarchs do exist in some developing democracies, for example, Thailand, and they may have opportunities and incentives to exercise strong political powers (Inata 2021). However, we focus on constitutional monarchs in advanced democracies.