A binder for an electric double layer capacitor electrode, which includes a copolymer (A) including monomer units derived from at least one compound (a) represented by the following general formula (1): CH2═CR1—COOR2   (1) wherein R1 represents a hydrogen atom or a methyl group, and R2 represents an alkyl group or a cycloalkyl group, the glass transition temperature obtained by homopolymerizing the compound (a) being less than 0° C., and monomer units derived from at least one compound (b) selected from acrylic acid alkyl esters, methacrylic acid alkyl esters, aromatic vinyl compounds, and α,β-unsaturated nitrile compounds, the glass transition temperature obtained by homopolymerizing the compound (b) being 0° C. or higher, wherein the total content of the monomer units derived from the compound (a) and those derived from the compound (b) is 90% or more by weight per 100% of the whole copolymer (A), and the glass transition temperature of the copolymer (A) is 10° C. or lower, which binder is excellent in smoothness, crack resistance and binding properties.