You can start with a deposit of $50 (¥5,000), or the equivalent in your account's base currency, which is the minimum for every deposit method. Trades start from $5 (¥500), so a first deposit of that size gives you room for a number of small trades while you get used to the platform.
A deposit of any amount also counts towards the welcome cashback bonus of $50 (¥7,500), which is credited after your first 20 trades. See Welcome cashback bonus for new accounts.
If you'd rather get a feel for the platform first, the demo account comes with ¥50,000,000 of virtual funds and uses the same prices as a live account, so you can practise for as long as you like before depositing. See How to use the demo account.
Trading involves risk, and many traders choose to keep each trade small in relation to their balance, which the minimum trade size makes easy to do.
Related: How to deposit · Deposit limits, fees and currencies · How to place a trade · Welcome cashback bonus for new accounts · How to use the demo account