Hi Hiroshi,
I am assuming that you are using MATLAB latest version. To generate the output signal on A2L file , you can follow any one of these approaches,
- you can mark the relevant output signal as "test point".
i. Select the output signal
ii. Open Property Inspector
iii. Check the Check-box for "Test point" (Highlighted in the figure below). 
Also you can follow this doc link
Where it is mentioned that:
"ASAP2 data definition is achieved with Simulink® data objects and test point signals. "
2. Alternatively you can create a simulink object for the relevant output signal with the storage class "ExportedGlobal".
Using both of the above approach you will be able to generate output signal on A2L file.
