Shopping with passport (1 year visa)?

I have visa 1 year, valid to 2015/07/20. But I will back to my country on 2015/02/20 (~6 months stay in Japan).

Can I shopping duty free in Japan?

Thanks so much.

If you say duty free shopping, you will make the purchase but you will leave with the item, unopened and unused, from Japan? The shops that offer duty-free shopping are limited in number in Japan, mostly to department stores and some electronics shops.

No. Only tourists with a "Temporary Visitor" visa can claim back taxes.

As green frog says, regardless of how long you stay, you're one year visa disqualifies you from tax free shopping at shops in Japan. You can do duty free shopping at the airport inside the security zone however.

Thanks so much. Maybe, I do shopping free duty at airport.

Does that place sell electric devices such as iPhone(unlocked), mobile phone (unlocked) camera...?

iPhone(unlocked) - no
mobile phone (unlocked) - no

camera - yes, but they will be the expensive international models

You'll save more money shopping the discount stores around Akihabara even with the tax.

Only those with less than 6 months' residence in Japan qualify for tax free shopping (the landing permission/residency status type doesn't actually matter). The tax free laws change in a couple of months' time and additional categories of things will be available tax free from that time. Doesn't help the OP though.