This electrolysis device is characterized in that: the device is provided with an electrolysis unit; the electrolysis unit is provided with a flow path for a fluid to be processed, at least one electrolysis electrode pair, an inflow opening, and an outflow opening; the electrolysis electrode pair is disposed so as to be inclined to the vertical direction and includes an upper electrode and a lower electrode disposed so as to face each other; and the flow path for the fluid to be processed is provided such that fluid flowing in from the inflow opening flows from a lower side to an upper side of an inter-electrode flow path between the upper electrode and lower electrode and flows out of the outflow opening.