Co-design is a design approach where people without design skills actively collaborate with people with design skills to create new products or services. This approach is widely used in Europe, especially Nordic countries, while it is not much developed in Japan. Cultural studies have identified major differences between Japan and Nordic countries. This paper explores the impact of Power Distance (PD), which illustrates way a person behaves in the presence of a person from a different “hierarchical” level, through a lab-based experiment: we observed the behaviour of groups with low or high PD scores engaged in creative design activities, and when a design expert joined the group or not. The findings show that, depending on the cultural background of the participants, their involvement in idea generation was affected by the presence of a designer. This work is expected to support the development of culturally-adapted methods for design collaboration and creativity.