Applications of an iterated hash function such as HMAC require that the compression function of the hash function is a pseudorandom function. However, the pseudorandom-function property of the compression function was not analyzed up to now. This paper shows that it is easy to distinguish between the 22 step-reduced SHA-512 compression function with the key-via-IV strategy and a random function. This is the first result on the pseudorandom-function property of the SHA-512 compression function with the key-via-IV strategy. A similar distinguishing attack is applicable to the SHA-256 compression function with the key-via-IV strategy.