Provided is the positive electrode active material for a potassium ion battery according to the embodiment comprises a compound represented by Formula (1), in which M represents at least one element selected from the group consisting of V, Fe, Co, Ni, and Mn, and x represents a number from 0 to 1; and is a positive electrode for a potassium ion battery comprising the positive electrode active material for a potassium ion battery according to the embodiment, or a potassium ion battery comprising the positive electrode for a potassium ion battery. KMOxPO4F1-x  [Formula (1)].