Synchronize contacts of a Google Account with an Apple Account I have a lot of contacts on my Google Account and I want to have them on a Mac. 

Is it possible to synchronize them with an apple already existing account? The apple account haven't the same mail of the Google Account.
You can add your Google account to your Mac, and enable the option to sync your contacts.  To learn more about adding your Google account, take a look here.

or

From an iPhone, follow these steps to set up contact syncing with Google Contacts:


Go to Settings > Mail, Contacts, Calendars > Add Account > Other > Add CardDav Account.
Enter the following information in the fields:

Server: google.com
User Name: Enter your full Google email address
Password: Your Google account password
Select Next at the top of the screen to complete the setup.
After you have completed the setup, open the Contacts app on your device. Syncing should begin automatically.


Note: Make sure that SSL is enabled (under Advanced settings), and that the port is 443.