The present invention relates to an in vivo radiation amount measuring instrument. An in vivo radiation amount measuring instrument according to the present invention comprises: a main body elongated along an in vivo inserting direction and capable of supplying a fluid； an expanding part having at least a portion thereof fixed or connected to the main body and capable of being expanded and contracted by means of the outflow/inflow of the fluid； and a radiation measuring part disposed on the expanding part and measuring the amount of surface radiation distribution on in vivo tissue which the expanding part contacts by expanding.
