According to the portable interdental toothbrush in accordance with to the present invention, when the interdental toothbrush is carried without using it, the cleaning solution is not discharged since the elastic ball disposed on the assembly protrusion of the cleaning solution tube is closely adhered to the outflow grooves and passing grooves, and, when it is used, the cleaning solution is discharged through the discharge hole, passes through the passing grooves, and reaches the brush since the elastic ball is separated and apart from the outflow grooves, whereby it is convenient to use and carry, it has a simple structure to enable mass production at a low cost, and it allows any user to use which promotes the dental and oral health for citizens.