An automatic foam soap dispenser includes a liquid soap dispenser, an activation unit, and an actuation unit. The liquid soap dispenser includes an outlet, a fluid reservoir for containing liquid soap, and a pump being depressed for dispensing the liquid soap in the fluid reservoir to the outlet. The activation unit includes a sensor for detecting a presence of a user of the liquid soap dispenser, and a motor having a transmission shaft, wherein the motor is activated by the sensor for generating a rotational power to the transmission shaft. The actuation unit includes a pressing member and a linkage system arranged to transmit the rotational power from the motor to a linear movement to the pressing member so as to drive the pressing member to depress the pump.