transferだけじゃなくてtransferFromがあるよ

✅ ERC20 has transferFrom and transfer

In the ERC interface**,** implement all available functions.
If you plan to create your own tokens, consider newer protocols like: ERC223, ERC721 (used by Cryptokitties), ERC827 (ERC 20 killer).
If you can, check for EIP 165 compliance, which confirms which interface an external contract is implementing. Conversely, if you are the one issuing tokens, remember to be EIP-165 compliant.
Remember to use SafeMath to prevent token under/overflows