An apparatus for verifying validity of transactions and/or blocks includes: a processor, a memory, and a communication device, wherein the processor executes a program stored in the memory to perform: verifying validity of a predetermined number of transactions and/or blocks among a plurality of transactions and/or blocks received from at least one peer in a blockchain system; and determining an increase or a decrease of the predetermined number according to a verification result of the predetermined number of transactions and/or blocks is provided.