An electromagnetic vibrational diaphragm pump comprising an electromagnet portion having an electromagnet arranged in a frame, a vibrator which is supported in the electromagnet portion and equipped with a magnet, diaphragms with a large diameter and diaphragms with a small diameter which are successively connected with both ends of the vibrator, and the pump casing portions of the diaphragms with a large diameter and diaphragms with a small diameter which are fixed on the both end portions of the electromagnet portion, wherein the left and right pump casing portions have pump chambers respectively corresponding to the diaphragms with a large diameter and diaphragms with a small diameter. Medium pressure (about 50 to 200 kPa) can be generated.