A binder, including a fluoropolymer, the fluoropolymer including a polymerization unit based on vinylidene fluoride and a polymerization unit based on a monomer having an amide group represented by —CO—NRR′ (R and R′ are the same as or different from each other and each represent a hydrogen atom or an alkyl group optionally having a substituent group) or an amide bond represented by —CO—NR″— (R″ represents a hydrogen atom, an alkyl group optionally having a substituent group, or a phenyl group optionally having a substituent group) and having a solution viscosity of 10 to 20,000 mPa·s. Also disclosed is a positive electrode mixture and a negative electrode mixture containing the binder, a positive electrode, a negative electrode and a lithium ion secondary cell.