Polysaccharide derivative

A polysaccharide derivative having a cationic group and a hydrocarbon group (R) having 2 or more and 22 or less carbon atoms,

• wherein:
• the cationic group is a quaternary ammonium salt, or a tertiary amine capable of being converted into a quaternary ammonium salt upon addition of a proton, and its quaternary ammonium salt;
• the hydrocarbon group (R) is bound to a group resulting from eliminating a hydrogen atom from a hydroxy group of a hydroxyalkylated polysaccharide via a group represented by the following formula (1):
• wherein:
• Z represents a single bond or a divalent hydrocarbon group having an oxygen atom;
• R represents a hydrocarbon group having 2 or more and 22 or less carbon atoms;
• and
• * represents a binding position to a group resulting from eliminating a hydrogen atom from a hydroxy group of the hydroxyalkylated polysaccharide;
• the hydroxyalkylated polysaccharide is a hydroxyethylated polysaccharide;
• the degree of substitution (MSR) of the hydrocarbon group (R) is 0.001 or more and 0.08 or less;
• and
• the hydroxyalkylated polysaccharide has a weight average molecular weight of 10,000 or more and 200,000 or less.