  We explore phenomenologies of the topflavour model for the LEP experiment at
$m_{_Z}$ scale and the atomic parity violation (APV) experiment in the $C_s$
atoms at low energies. Implications of the model on the $Z$ peak data are
studied in terms of the precision variables $\epsilon_i$'s. We find that the
LEP data give more stringent constraints on the model parameters than the APV
data.
