"I copied the model. And then when I modify it, it also makes changes to the original one."

In this case, you want to [Clone] the model, not [Copy]. You can find how to clone models in this blog, though we still get some inquiries like one on the top, so I am going to write down about it with some updates.

- How to clone models

Let's clone the ER Entity0. ER Entity0 has Attribute0 and Attribute1.











Right-click on Entity0 to open its Pop-up menu and then click [Clone].




























Cloning Entity0 succeeded. The cloned model is Entity0_0. Attributes of Entity0's would get cloned also and modifying Entity0_0 or its Attributes do not affect the original models.















Models that you can clone in astah* professional and UML
Package, Subsystem, Model, Class, Attribute, Operation, UseCase, Actor, Interface, Entity, Boundary, Control, Component and Node

Models that you can clone in astah* professional only
ER Entity (Primary key, Attribute), Domain, Datastore, External Entity, Requirement and TestCase

Cheers,
Satomi