Japan's wholesale prices dropped for the 20th straight month in November, down 2.2% from a year earlier, weighed down by lower crude oil prices, Bank of Japan data showed Monday. 
The result underscores that the Japanese central bank faces a difficult challenge to achieve its 2% inflation goal, according to Japan's News Agency (Kyodo). 
Wholesale prices tend to affect consumer prices, which have stayed in negative territory in recent months. 
Prices of petroleum and coal saw a 5.7% fall, and those of nonferrous metals slid 5.4%. 
Prices of electricity, gas and water marked a 10.8% drop, while those of chemical products saw a 5.8% fall.