A novel type A botulinum toxin preparation is provided. A neuromuscular transmission blocking agent comprising as an active ingredient a highly purified type A botulinum toxin from Clostridium botulinum as infant botulism pathogen and a medicament for treating a disease with a muscle overactivity comprising as an active ingredient said toxin. In particular, the medicament of the present invention, as compared to the conventional known botulinum toxin preparations, has rapid efficacy of potential and is less diffusive and thus, having a broader safety margin, may be used as therapeutic medicament for decreasing local, muscle overactivity in a disease with a muscle overactivity.
