A hidden braking device comprising a brake handle, a brake member adapted to control a rotation of a wheel set, a connecting member connected to said brake handle and said brake member, and a main frame disposed between said brake handle and said wheel set, wherein said connecting member is disposed inside said main frame, said main frame including a lower frame and an upper frame sliding relative to said lower frame to attain an adjustment of a full length of said main frame, said connecting member including an upper stem connected to said brake handle and a lower stem connected to said brake member, characterised in that said connecting member includes a locking set disposed at an end of said lower frame where said upper frame is inserted and an adjusting set connected to said upper stem and said lower stem, said upper stem including a sliding trough adapted for an insertion of said lower stem and a fixing trough with a plurality of fixing notches formed on a surface of said sliding trough, said locking set including a locking body disposed on said end of said lower frame and a locking unit pivotally connected to said locking body and capable of triggering a movement of an operating unit of said adjusting set, said adjusting set including a fixing rod disposed on said lower frame, a main base fixed to said fixing rod, said operating unit movably disposed inside said main base and adapted for insertions of said upper stem and said lower stem, a positioning case connected to said lower stem and located in said operating unit, an engaging case disposed relative to said positioning case, an elastic unit disposed between said positioning case and said engaging case and having a first end and a second end engaged with different ones of said plurality of fixing notches, and a first spring unit disposed on said operating unit and capable of pushing said operating unit to said engaging case to thereby position said engaging case, said engaging case including a first engaging part capable of restricting said first end of said elastic unit and a second engaging part capable of restricting said second end of said elastic unit when said main frame operates the adjustment of said full length. said connecting member including an upper stem connected to said brake handle and a lower stem connected to said brake member, characterised in that said connecting member includes a locking set disposed at an end of said lower frame where said upper frame is inserted and an adjusting set connected to said upper stem and said lower stem, said upper stem including a sliding trough adapted for an insertion of said lower stem and a fixing trough with a plurality of fixing notches formed on a surface of said sliding trough, said locking set including a locking body disposed on said end of said lower frame and a locking unit pivotally connected to said locking body and capable of triggering a movement of an operating unit of said adjusting set, said adjusting set including a fixing rod disposed on said lower frame, a main base fixed to said fixing rod, said operating unit movably disposed inside said main base and adapted for insertions of said upper stem and said lower stem, a positioning case connected to said lower stem and located in said operating unit, an engaging case disposed relative to said positioning case, an elastic unit disposed between said positioning case and said engaging case and having a first end and a second end engaged with different ones of said plurality of fixing notches, and a first spring unit disposed on said operating unit and capable of pushing said operating unit to said engaging case to thereby position said engaging case, said engaging case including a first engaging part capable of restricting said first end of said elastic unit and a second engaging part capable of restricting said second end of said elastic unit when said main frame operates the adjustment of said full length.