A bicycle air pump includes an air cylinder; a joining member on the cylinder and including upper, intermediate and lower chambers, and a passageway communicating the cylinder with the lower chamber and a relief valve; an activation assembly on the joining member and including a hollow spring-loaded stem in both the intermediate chamber and the lower chamber, an end seal, a cap on the upper chamber, a push rod through the cap to urge against the seal and having an axial hole and a lateral hole communicating with the axial hole, a knob secured to the push rod and the cap, and an outlet; a pressure gauge on the joining member and communicating with the passageway; an inlet assembly secured to bottom of the cylinder and including a check valve; and a blocking member secured to bottom of the stem for blocking the passageway when in an inoperative position.