Is Bhikkhu allowed to keep his food in refrigerator for next day or for long period?
Is Bhikkhu allowed to keep his food in refrigerator for next day or for long period?
Not proper food, only certain types of edibles:

The Four Sorts of Edibles
Any nutriment that a bhikkhu puts into his mouth is classified in four
groups, which specify the time limits during which he can consume or
store them:
(i) Food — Limited from Dawn to Noon (Yaavakaalika)
(ii) Fruit juices — Limited to One Day (Yaamakaalika)
(iii) Medicinal-tonics — Limited to Seven Days (Sattaahakaalika)
(iv) Other Medicines — For All One's Life (Yaavajiivika)
-The Bhikkhus' Rules: A Guide for Laypeople

This is also what I've seen in some western monasteries.

Is this common sight to see a refrigerator in a monk's room in Theravada monastery?
The few times I've been in a monk's private room, I never saw one. But in the same housing (under the same roof), it's common.