A variable displacement oil pump includes: a variable displacement mechanism that is able to change a discharge amount per rotation of an input shaft. The variable displacement mechanism includes a pump housing, an oil pressure chamber provided in the pump housing, and a capacity adjustment member displaced by oil pressure from the oil pressure chamber. The capacity adjustment member is configured to be operated when receiving control oil pressure that is supplied from a control valve to the oil pressure chamber. The pump housing has an oil release hole that is opened to face the oil pressure chamber and that penetrates a wall section of the pump housing to partially release oil.