I've just joined a company. Its my first job. I want to start my own business as soon as possible. So how much experience is needed to start one's own business?

Hi...good question, you really do not need experience to start a business to be honest...all you need is determination and the desire to own your own business and be successful. Having experience in what you are doing helps but having a good customer service attitude and wanting to make your customer's happy and meet/or exceed expecations is the best experience.
You will need to know about taxes, employment law (if you will hire people) and other business things...but honestly, these can be learned as you go and as needed.Good luck! Pasting in a link and some of the content below for your reference.

http://www.wikihow.com/Start-a-Small-Business
Are you one of those who dream of owning your own business? You'll be your own boss, and the captain of your destiny—–maybe even a captain of industry. Is it hard? Without a doubt. Is it challenging? Absolutely. Do you have to be wealthy and well-educated with a lengthy resumé? Not at all! Can you do it? As the magic 8-ball says, "All signs point to yes!" So how do you do it, and make it work? Plan, plan, plan! There are some tried and true ways head down the path of creating your own business, and there is no time like the present to get started!

Hi Nihar,
What kind of business do you want to start? I agree with Gary, you technically don't need experience to start your own business, just a great idea and an insanely hard work ethic! But, I will say that the more experience you have in the career field you want to start a business in, the better. If, for example, you want to open up a clothing store, I highly recommend working in retail/managing a clothing store before doing so. The more you know about the business the more successful you will be.