I used 'Screen Reader', which can be downloaded from Chrome Web Store. So, other screen readers cannot act in the same way the program does.
I was quite confused when I compared the two things. Luckily, I found out the difference.
If other elements' id values are written as their values, then, elements of them sound the element's content.
"labelledby" does not sound its element's content, while "describedby" does sound its element's content.
Click the buttons and check the difference.