In Astah's ER diagrams, you can set the display level of ER Entities as you wish.
For example, we have one ER Entity as figure below.








And you can select the level of displayed information in ER Entities from the following three.
1) Entity
2) Primary Key
3) Attribute



How to do so:
There are three ways to do so.

(1) Best if you want to set it per ER Entity

Right-click ER Entity and go to [Display Level]

(2) Best if you want to set it for all the ER entities in entire project

Go to [Tool] - [System Properties] - [ER Diagram] - [Display Level]








(3) Best if you want to set it for all the ER Entities per ER diagram

Select the ER diagram in the structure tree and go to its Property View (The left bottom pane in Astah) and then set it from "Initial Display Level"












Furthermore, you can show/hide each Primary Key/Attribute per each ER Entity.

1) Right-click ER Entity and select [Attribute Visibility]
2) [Attribute Visibility Chooser] dialog appears, tick or take it off on the left of Attributes to show/hide them






This customizability of display level should help making your diagrams more expressive with essential information by hiding unnecessary information for your needs and purposes.

Best,
Satomi