is it possible show custom message in product detail page?

Hi,

Well, there are solutions.
Are you saying that for all your products, you don't want to display the quantity input field next to the product add to cart button ?
And you want to display a message from a custom field of the table "product" on the product page ?
To hide the quantity input field, you can set the "quantity input method" setting to "none" in the HikaShop configuration. If it's only for some products, you have a "quantity input" setting in each product in order to override the setting in the HikaShop configuration.
To display the content of a custom product field on the product page, there is a "front" display setting in the custom field settings page. Now, if you want to display the content of the custom field in a specific area of the product page, you'll have to edit the product / show_default view file via the menu Display>Views and add a bit of custom code where you want it to appear.
For example:

<?php echo $this->element->xxx; ?>