A fuel supply apparatus includes a component adjustment unit, a low-pressure side passage, and a valve. The unit adjusts component composition of fuel by separating a particular component from fuel. The unit includes a component separation wall, which divides an interior of a portion of a fuel supply passage between an anterior chamber and a posterior chamber. The wall includes a separation membrane, which the particular component of fuel in the anterior chamber selectively permeates to be separated. The particular component after passing through the wall is temporarily stored in the posterior chamber. When the low-pressure side passage connected to the posterior chamber is opened by the valve, the particular component is separated. Fuel, from which the particular component is separated, is supplied to an injection valve from the anterior chamber. When the low-pressure side passage is closed by the valve, the separation of the particular component is restricted.