A node device on a blockchain network is provided. The node device includes a blockchain state monitor that calculates an estimated time of transaction processing completion according to a transaction cost by using state information about the blockchain network, a transaction cost determiner that calculates a minimum transaction cost that satisfies a user's requirements by using the calculated estimated time of transaction processing completion, and a transaction processor that processes a transaction of the user in response to a first transaction processing request when the first transaction processing request, which pays a transaction cost equal to or greater than the minimum transaction cost, is generated by the user.