To obtain a thermoplastic biodegradable plastic having a specific chemical structural formula, not requiring the use of a melting point imparter such as a specified biodegradable polymer, biodegradable plasticizer, or the like, useful as a binder for bonding a biodegradable cellulose-based material, effective for the maintenance of the global environment.

This thermoplastic biodegradable plastic has a chemical structural formula of formula I [R is H, a group of formula II or a group of formula III ((m) is 2-16)] comprising a cellulose as a molecular skeleton. The degree of substitution of benzyl group or alkaroyl group for OH groups in the cellulose molecule skeleton is 0-3. The objective plastic is preferably a benzylated cellulose which is formed by reacting a cellulose with benzyl bromide or a lauroylated cellulose which is formed by reacting a cellulose with lauroyl chloride.