I'm a beginner who wants to play the piano. I'm going to take some teacher's lesson so I need an authentic keyboard (as maximum authentic as it possible). Unfortunately, I can only afford something about 1800$.
Prices on Yamaha clp 320 and casio ap 620 are about the same.
What digital piano ,in your opinion, would be better for me?Casio ap is new so won't be there any technical problems with it?
I don't need any special technical features in it. Only keyboard and sound.

P.S. Thank you for help and sorry for poor English.

I suggest you take the one you like.
Yamahas keyboard is more on the lighter side and Casios is more on the heavier.
I think they should both do just fine, as long as you choose the one that you like the most.
You should also try some Rolands, like the HP 201, the weighth of the keys is somwhere in between, but it has a more round, rich and mellow sound.
You could probably get a cool Kawai too for that money.

If I compare them I find AP-620 to be the better (and slightly newer):

AP-620 :

• 4-level sampling
• Graded Hammer + Tri-Sensors (for faster response)
• 250 voices (instruments/tones)
• Reverb, chorus, brilliance, acoustic resonance
• Speakers 30W * 2

CLP-320:

• 3-level sampling
• Graded Hammer (only)
• 10 voices (instruments/tones)
• Reverb
• Speakers 20W * 2

There are more features not exactly covering each other, but mostly it is in the favor of the AP-620.

Thank you so much!
But the casio ap 620 is a new piaono. So won't be there any problems with it? And what can you say about their keyboards?

^But still, he should deffinately try them both and than decide.
I would still go for the Roland, personally.

Ok. What is about Rland. I don't know about it too much. Do yo have one? Which model I have to look on?

Well, I only have a synth (EXR 5s) but I'm looking into buying one, probably the HP 203, or I'll wait for the new series...
For your budget, you should be looking into the HP201, it's just a tiny bit pricier than the CLP 320 here.
It's basically the same concept with a bit more features, but I personally prefer the Roland sound and touch.

Vid_w: The Roland HP201 puts up a fair fight with the Casio AP-620:

Link to AP-620
Link to Roland HP201

Both have nice values. I would try them out in a shop side by side, listening both to their speakers and with a pair of quality Hi-Fi headphones.

Though Casio AP-620 has a 200 more voices/instruments than the Roland HP201.