Hi @sunghoon123!
Oh no! If there has been absolutely no purchases or transactions in your account activity but the balance amount changed, do you possibly have more than one currency active on your account? If so and you hold a balance the AUD balance amount will fluctuate depending on that day's market value for any other currency balance you might carry.
If this is not the issue and there are no transactions in the account activity to explain the difference, then I would encourage you to contact our customer service to investigate this matter for you. To do this, please follow the Help & Contact link at the bottom of the page, or you can also reach us on Facebook or at @AskPayPal on Twitter.
I hope this helps and thank you for joining the Community!
Michelle
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