The outbreak of COVID-19 in Japan – the first country to officially report a case outside China – was an opportunity to revive the debate on the relationship between policymakers and scientific experts. The latter, selected and convened in a committee by the government, played a very important role in defining policy responses to coronavirus and in risk communication to the Japanese public. Criticism then fluctuated between the denunciation of a so-called “government of experts” lacking democratic legitimacy (scientifization of politics) and that of “experts at the mercy of the government” whose scientific legitimacy had been manipulated (politicization of science). In order to go beyond these two archetypal representations, this chapter analyses in detail the ways in which experts and their opinions were integrated into the decision-making process, as well as the reactions of the actors involved in the Japanese political and media ecosystem during the COVID-19 pandemic. To do so, this study draws on the literature on knowledge brokers – intermediary actors between science and politics – and on official documents (reports, legal texts, etc.), press articles and testimonies of experts and political actors. This study shows that the relationship between experts and policy-makers was built in a trial-and-error manner, with readjustments according to the balance of power, the perception of their respective roles, as well as the ambivalent and paradoxical reactions of the media, the public and some external specialists. In this context of uncertainty and high “social request for expertise”, although political actors have relied on experts as an essential source of legitimacy for their decisions, the latter have not hesitated to express their disagreements with the government, as well as to demand a clearer division of responsibilities and more transparency, in order to create a decision-making process that would be both more attentive to scientific research and more democratic.