There is mini recording devie for a clear recorded sound at a distance of 4 meter.for a class room lecture.?

at a distance of 4 meters, your problem is not the device, it will be room echo, air-conditioner/furnace air blowers, sounds of students talking, shuffling papers, even outside traffic if the windows are open. you need to get the pickup from very close to the lecturer. A savvy instructor usually will allow students to place their pocket recorder devices on or near the lecturn.There is mini recording devie for a clear recorded sound at a distance of 4 meter.for a class room lecture.?
I have a Zoom H2 Handy Recorder which I use for many recording tasks. I think it would work well for that. to improve the recording you could plug in an external shotgun microphone. or get a wireless lavalier microphone and convince the lecturer to wear it. But these options might be a bit pricier than your application justifies. some of the less pricey digital recorders might work, but I have no experience with them and haven't researched the characteristics of their built-in microphones. at a distance of 4 m you'd probably want to set the microphone gain setting pretty high.