Living expense in japan

What is the ideal salary to live in a city like Tokyo for a couple with one kid of age 1.

Tokyo is not a city. Where in Tokyo?

Tokyo prefecture has 23 special wards and 39 cities. Greater Tokyo includes Chiba, Kanagawa and Saitama. Some people commute from further than that, so you might want to be a little more specitic.
Cost of living ranges from hugely expensive (Minato for example), to "cheaper" further out. You can spend as much as you want, but I suspect you will not be renting a 4,000,000 yen/month apartment if you are posting on this forum (you can spend more).

Say, 300,000 yen in hand (after paying taxes). A guideline by a life insurance company is a monthly income of (age) man yen. 1 man yen = 10,000 yen and the mean age with a kid of age 1 would be 30. Taxes would be roughly 20 percents, thus, 360,000 yen from a company.

The mean annual income for the thirties is in a range of 3 to 5 million yen. Their desired annual income falls in a range of 5 to 7 million yen. With this factor in mind, the ideal monthly income would be 500,000 yen.
http://investment-beginner.com/family/cpmpare/average/

Living costs are the sum of housing, goods, and transportation. The first two are more expensive in the central Tokyo, but the last one cheaper. The company may cover the transportation cost, but you have to pay your time for commuting. All individual have to seek their own best balance. Families with kids prefer to live in the suburbs, while singles live in the center. The government sets a guideline among areas. The central Tokyo (special 23 wards) is rated as 20% more.
http://www.mhlw.go.jp/file/05-Shingikai-12601000-Seisakutoukatsukan-Sa...