Long-lived qubits do not easily couple with a measurement apparatus because they are usually well-isolated from
any other system. There is sometimes difficulty in implementing reliable projective measurements on such long-lived qubits.
Spin amplification using many ancillary qubit, where the ancillary-qubits state changes depending on the target-qubit state,
is one of the promising ways to construct a high-fidelity measurement on such a system. We show that a fast and accurate
amplification is possible even in the presence of the inhomogeneity of the coupling and frequency of the ancillary qubits. The
scheme can be realized with a simple experimental setup where the target qubit is collectively coupled with many ancillary
qubits. Our scheme is robust against realistic imperfections so that this could provide a new way to readout a single spin that
could not have been measured in the previous approaches.