A device for assembling a turbine engine is configured for centering a shaft of a second module relative to a longitudinal axis of a hollow hub placed in front of a first module, the first module including a longitudinal cavity opening at the front into the hollow hub and passing through the first module until a rear end, the shaft configured to be inserted into the longitudinal cavity. The device includes a centering element and a guiding tube. The centering element is configured to be placed in the hollow hub. The guiding tube is configured to enter into at least one portion of the longitudinal cavity of the first module. The device is arranged so that the guiding tube slides inside the centering element. The invention also relates to the assembly formed by the device and a calibration jig, as well as an assembly method using same.