The average income of national lawmakers fell 6.5 percent in 2015 from a year earlier to ¥22.69 million for the first decline in four years, the Diet reported Monday.
The top earner was Miki Watanabe, an Upper House member and founder of Watami Co., which operates a chain of izakaya pubs, but he saw his income decline by more than ¥1 billion last year, which brought down the Diet-wide average.
The report covering 714 lawmakers also showed that average income from stock dividends fell by ¥1.12 million to ¥2.73 million.
A 20 percent reduction in the salaries of Diet members had been applied from January through April 2014 in a bid to win public acceptance for the consumption tax hike, which was implemented that April 1, but lawmakers received their full salaries throughout 2015.
The number of lawmakers who earned more than ¥50 million came to 19, down three from 2014.
Watanabe, of the ruling Liberal Democratic Party, reported ¥151.72 million in income in 2015, compared with ¥1.28 billion a year earlier.
The second-biggest earner was Mitsunari Okamoto, a Lower House member of the junior coalition party Komeito, with ¥91.74 million, followed by Masayoshi Shintani, a Lower House member of the LDP, with ¥81.95 million.
By party, members of Seikatsu no To (People's Life Party) earned the biggest average of ¥27.37 million, followed by Osaka Ishin no Kai members who reported an average of ¥24.95 million and LDP members with ¥23.57 million.
The main opposition Democratic Party placed fifth among the nine parties with seats in the Diet, with its members reporting an average of ¥20.89 million.
The report covers 472 Lower House members and 242 Upper House members who had seats in the Diet for the whole of 2015.
The incomes of Lower House members averaged ¥22.94 million, while those of Upper House members came to ¥22.20 million.