  We consider a communication system where a relay helps transmission of
messages from {a} sender to {a} receiver. The relay is considered not only as a
helper but as a wire-tapper who can obtain some knowledge about transmitted
messages. In this paper we study a relay channel with confidential
messages(RCC), where a sender attempts to transmit common information to both a
receiver and a relay and also has private information intended for the receiver
and confidential to the relay. The level of secrecy of private information
confidential to the relay is measured by the equivocation rate, i.e., the
entropy rate of private information conditioned on channel outputs at the
relay. The performance measure of interest for the RCC is the rate triple that
includes the common rate, the private rate, and the equivocation rate as
components. The rate-equivocation region is defined by the set that consists of
all these achievable rate triples. In this paper we give two definitions of the
rate-equivocation region. We first define the rate-equivocation region in the
case of deterministic encoder and call it the deterministic rate-equivocation
region. Next, we define the rate-equivocation region in the case of stochastic
encoder and call it the stochastic rate-equivocation region. We derive explicit
inner and outer bounds for the above two regions. On the
deterministic/stochastic rate-equivocation region we present two classes of
relay channels where inner and outer bounds match. We also evaluate the
deterministic and stochastic rate-equivocation regions of the Gaussian RCC.
