An air spring for railroad cars includes an air spring part formed by an upper support on a vehicle body side, an intermediate support arranged therebelow, and a diaphragm made of rubber and extending between the upper support and the intermediate support; and an elastic mechanism b formed by a rubber mass 5 interposed between the intermediate support and a lower support 4 on a bogie side arranged therebelow. The rubber mass 5 has an end in contact with the lower support 4 formed as an enlarged end 5A increasing in diameter as approaching the lower support 4 in a vertical direction. An outer circumferential portion of this enlarged end is fitted in and bonded to an annular groove 12 formed in the lower support 4, and the annular groove 12 has an annular bottom 12A inclined to decrease in height radially outwards to have an annular tapered bottom 12a.