A controller capable of improving the disappearance resistance of a synthetic resin coating of a diaphragm, and a vaporization supply device comprising the controller. The controller includes a body having an inflow passage and an outflow passage, a valve seat provided between the inflow passage and the outflow passage, a diaphragm capable of being seated on or separated from the valve seat, and an actuator for causing the diaphragm to be seated on and separated from the valve seat. The material of the valve seat is nickel-based, and the diaphragm is provided with a synthetic resin coating on a surface of a side to be brought into contact with the valve seat.