1. An image processing apparatus which imposes a usage restriction on an included function according to access control information for each user, and executes processing for a permitted user, comprising: a setting unit which sets a condition required to release the usage restriction of the included function; a determination unit which determines whether or not a processing request from a user to a usage-restricted function satisfies the condition required to release the usage restriction; a generation unit which generates, when said determination unit determines that the processing request satisfies the condition required to release the usage restriction, restriction release information required to temporarily release a restriction of the usage-restricted function; an execution unit which releases the restriction of the usage-restricted function based on the restriction release information generated by said generation unit, and executes processing by the function; and a discarding unit which discards the restriction release information based on a discarding condition of the restriction release information after said execution unit executes the processing.