Short answer: Zacharias Jansen
Long answer: Your question is not valid for 2 reasons:
1. You cannot "discover" something if it does not exist. You should be asking who invented it, not who found it laying around somewhere.
2. A "simple microscope" is not common terminology. Simple compared to an electron microscope? or simple compared to a compound microscope?
What is typically referred to as just "microscope" is technically a compound microscope. A set of multiple lenses mounted in a desktop style that allows the compounding of magnification.
A compound microscope is the standard microscope in any basic lab setting.
Anything more "simple" than a compound microscope would not even really be a microscope, it would either be a telescope, or simpler than that is a magnifying glass (with a single lens)
The inventor of the magnifying glass was: Roger Bacon
The next step up is the telescope invented by: Zacharias Jansen
The next step up is the "compound microscope" which was also invented by: Zacharias Jansen (this is the simplest form of what would be recognized as or named "microscope")
If you wanted to go even "simpler" and define microscope as anything that magnifies, there were reading glasses around for thousands of years prior, and even "reading stones" which were lumps of polished glass used to magnify parchment in Egypt as far back as 7000 B.C. (inventor unknown).
So it really depends on how you wish to refine your meaning of simple. The magnification of anything? There is no known inventor for reading stones, his name is lost to time. Or if you mean the first invented microscope that could examine things too small for a human eye to detect, that's a compound microscope.
Thus if I am guessing your meaning correctly, you meant to ask this question:
Question: Who invented the compound microscope?
Answer: Zacharias Jansen
it was discovered in the year 1595
Janne B. Arnaiz ^^
The first scientist credited with the invention of the microscope is Zacharias Janssen, a Dutch spectacle maker, around the late 16th century. His compound microscope had two sets of lenses that allowed for greater magnification than simple magnifying glasses.
He made his first simple lens microscope in 1595.
1590s
He first discovered the cell with his simple microscope.
Van Leeuwenhoek.
The simple microscope was very important in discovering cells. The compound microscope gave even more information.
simple or dissecting microscope -
The simple microscope was invented by Dutch scientist Antonie van Leeuwenhoek in the late 17th century. He used his handcrafted lenses to observe minute living organisms, revolutionizing the field of microscopy.
Robert Hooke in the year 1665 discovered the primitive microscope .
it was discovered in the year 1595
Zacharias Janssen discovered the compound microscope
Janne B. Arnaiz ^^
compound microscope
AnswerIt is said that Anton van Leeuwenhoek discovered it
Robert Hookes microscope had either two or more lenses. a simple microscope has one lens in it.