1. An image coding device comprising: image analyzing means for analyzing an input multi-level image; update value generating means for generating update information to be used when a probability estimation value is generated on the basis of adjoining pixel information as a result of the analysis by said image analyzing means; probability estimating means for generating a probability estimation value on the basis of the update information generated by said update value generating means and the result of the analysis by said image analyzing means; and code word generating means for arithmetically coding the input multi-level image on the basis of the probability estimation value generated by said probability estimating means.