An attachment coupling device is designed to releasably connect a variety of attachments to an arm and a push link of heavy machinery such as hydraulic excavators. The attachment coupling device comprises a pair of mounting brackets fixedly secured to the attachment, each bracket having first and second hooks spaced apart with each other. Another major element of the coupling device is a coupler which includes, a fixed plate affixed to the arm and the push link, a pair of fixed coupling pins each protruding outwardly from the fixed plate for engagement with the first hook of each of the mounting brackets, a pair of movable coupling pins for movement between a retracted release position and an extended coupling position wherein the respective one of the movable pins comes into engagement with the second hook of each of the mounting brackets, and an actuator for causing movement of the movable coupling pins.