I solved it by reinstalling Electrum.

Actually, the line was disconnected when receiving transfer.
It seems that synchronization did not complete due to some bug of the client.

Thank you TryNinja!!

I found a private key!

What should I do after this?

It seems that I can not receive BTC,because I forgot to press "SAVE" when creating receiveing address.
That address does not remain in the history of "Adresses".
However, the signature can be authenticated.
And "Synchronizing..."is appiering.


What can I do this?

Bitcoin Client Software and Version Number:Electrum 2.7.17
Operating System:Win8.1
System Hardware Specs:CPU/Intel i7-4770  RAM/8.0GB
Any Related Addresses:   1DQfFSswKyzpzrdWfUuwCikiuzyNbYYE9Q
Any Related Transaction IDs: