A modular building formwork apparatus comprising: a formwork wall including a wall plate and a frame disposed on said wall plate, and at least one interlocking device, characterized in that: said frame has at least one aligning hole and a locking hole; said at least one interlocking device including a housing unit, a rotation transferring unit, a transmitting unit and a locking member, said housing unit being securely disposed on said frame, said rotation transferring unit being disposed within said housing unit and having an input shaft which extends along and is rotatable about a first axis, and an output shaft which extends along a second axis that is perpendicular to the first axis and extendable through the at least one aligning hole, said output shaft being rotatable about the second axis with the rotation of said input shaft, said transmitting unit being coupled with and movable relative to said output shaft along the second axis and being rotatable about the second axis with the rotation of said output shaft, said locking member being coupled with said transmitting unit, and being movable along and rotatable about the second axis with the movement and rotation of said transmitting unit, said locking member having a head portion which is coupled with said transmitting unit along the second axis, a positioning portion which extends from said head portion along the second axis and away from said transmitting unit, characterized in that said locking hole has an internally threaded section and in that said locking member has a threaded portion which extends from said positioning portion along the second axis and away from said head portion, said locking member being insertable into the at least one aligning hole, said threaded portion being configured to permit mating engagement with the internally threaded section of the locking hole. said frame has at least one aligning hole and a locking hole; said at least one interlocking device including a housing unit, a rotation transferring unit, a transmitting unit and a locking member, said housing unit being securely disposed on said frame, said rotation transferring unit being disposed within said housing unit and having an input shaft which extends along and is rotatable about a first axis, and an output shaft which extends along a second axis that is perpendicular to the first axis and extendable through the at least one aligning hole, said output shaft being rotatable about the second axis with the rotation of said input shaft, said transmitting unit being coupled with and movable relative to said output shaft along the second axis and being rotatable about the second axis with the rotation of said output shaft, said locking member being coupled with said transmitting unit, and being movable along and rotatable about the second axis with the movement and rotation of said transmitting unit, said locking member having a head portion which is coupled with said transmitting unit along the second axis, a positioning portion which extends from said head portion along the second axis and away from said transmitting unit, characterized in that said locking hole has an internally threaded section and in that said locking member has a threaded portion which extends from said positioning portion along the second axis and away from said head portion, said locking member being insertable into the at least one aligning hole, said threaded portion being configured to permit mating engagement with the internally threaded section of the locking hole.