Connect the iPod shuffle

iPod shuffle を Mac に接続したらこんなメッセージが。

The iPod "iPod shuffle" is synced with another iTunes library. An iPod can be synced with only one iTunes library at a time. What would you like to do?
"Erase and Sync" replaces the contents of this iPod with the contents of this iTunes library.
"Transfer Purchases" copies iTunes Store purchases this computer is authorized to play from this iPod to this iTunes library.
Do not ask me agin
(Cancel) (Transfer Purchases) (Erase and Sync)

もちろん Cancel ボタンをクリック。