It doesn't have one, but it does have a permanent strainer.
On the forward end of the engine, below the drive pully for waterpump and alternator is a "key" arrangement which should be turned several times every time you use the engine, it consists of numerous fine metal plates on a spindle.
The service manual says that it should be overhauled every 100 hours (undo the 3 bolts, take the strainer out and flush it with clean oil when you do an oil change - drain the oil first) and replaced every 500 hours.
It does not have an external filter. There is an internal filter comprising a set of plates. This can be found on the front of the engine lower right hand side. If I remember correctly it looks like an old clockwork key and should be rotated at regular intervals. Do not have the engine anymore and cannot find old reference books but any Yanmar agent will advise.