Fibrous cellulose composite resin and production method therefor

A fibrous cellulose composite resin comprising:

• fibrous cellulose, a resin, and an acid-modified resin,
• wherein part or all of the fibrous cellulose is microfiber cellulose,
• the microfiber cellulose has hydroxyl groups, part or all of which are each substituted with a carbamate group, and has been defibrated into an average fiber width of 0.1 μm or larger, an amount of a byproduct generated in the substitution with a carbamate group is 10% or less per 100 parts by mass of a carbamate-modified cellulose obtained through washing, and
• the amount of the byproduct is measured by diluting the reaction product obtained by carbamate-modification reaction of urea and the fibrous cellulose with distilled water to have a solid concentration of 1%, mixing and stirring in a mixer, dewatering by means of a No. 2 paper filter and a Buchner funnel, repeating washing operation from the diluting to the dewatering twice, drying the obtained solid material at 105° C. for 6 hours to provide the carbamate-modified cellulose obtained through washing, and calculating amount of the byproduct by subtracting the amount of the carbamate-modified cellulose from the amount of the reaction product obtained by the carbamate-modification reaction.