My static IP and adsl connections are in same broad band line. I have an apache server installed in the lan with private IP. When we access the web server from external adsl line it is worked perfectly. Even though when we access the web server through the lan computer request is gone upto the gateway(router).
Please let me assist to resolve this problem

Great reference DaveArmour.

If the router does not support this, this alternative is to simply access the internal host for within the internal network using its internal IP instead of the external WAN IP or you'd have to get a router that supports this feature. Some do, and some don't provide this support.