Arduino for STM32

Hi,

I have a STM32VLDISCOVERY board and I want to use it as Arduino.
https://www.st.com/ja/evaluation-tools/ ... overy.html

This board seems to have supported Arduino for STM32, but I can't connect it via onboard USB.
I think I need proper bootloader for it.

Could you tell me how to find (or porting ?) bootloader for STM32VLDISCOVERY ?

I could upload Arduino .ino.bin file to STM32VLDISCOVERY via ST-Link but I want to deploy directly via Arduino IDE.

The F100 has no buitlin bootloader supporting DFU, so yes you should use a dedicated bootloader for this.
But AFAIK, there is no one supporting it.
You can try to build one using Roger's bootloder repo
https://github.com/rogerclarkmelbourne/ ... bootloader
or HID one from vassilis:

https://github.com/Serasidis/STM32_HID_Bootloader

Does the VLDISCO (F100) support USB at all ?

The USB plug on the board is for the onboard ST-Link-V1 debugger

/Bingo