I tried a solution but that doesn't work.
After then, I tried ssh ubuntu@{public IP} , I got ubuntu@{public IP}: Permission denied (publickey)
and I checked a debug too
...
debug1: Trying private key: C:\\Users\\{User}/.ssh/id_dsa
debug3: no such identity: C:\\Users\\{User}/.ssh/id_dsa: No such file or directory
debug2: we did not send a packet, disable method
debug1: No more authentication methods to try.
ubuntu@{public IP}: Permission denied (publickey)
I couldn't access. I think it's still find pem file.
So How could I access without pem file?
Looks like you don't have your local PC keypair needed for ssh handshake.
Try to generate it on your PC, and login again:
ssh-keygen -o