Dear Choton,
You have not explained why the need arises for your query. Isn't that your present employer refused to give a certificate of experience? Normally, an Experience Certificate is issued when one leaves any organization. In your case, you are still in employment and you wish to attend an interview, and you require a certificate of employment from your present employer to be shown to them, am I correct? First, ask them for such a certificate, and when refused, then you can show your appointment letter and other documents like a bank passbook, etc. Acceptance of these circumstantial evidences depends on the requirement of your prospective employer. You cannot take them for granted. For instance, when your competitors produce valid certificates, you, without such a certificate, how can you be preferred? But still, exceptional candidates can be selected, and appointment could be reserved subject to the production of necessary credentials. Don't panic, try to obtain and give it a try. All the best.