We report on the discovery of a transient X-ray pulsar , AX J1841.0 - 0536 , serendipitously found in the Scutum arm region with the ASCA in two separate observations .
The X-ray flux is very faint at the beginning , but exhibits two flares in the second observation .
The flare flux increases by a factor 10 within only \sim 1 hr .
Coherent pulsations with a period of 4.7394 \pm 0.0008 s were detected in the brightest flare phase .
The X-ray spectra in the quiescent and flare phases were fitted with an absorbed power-law model with a photon index \sim 1 plus a narrow Gaussian line at the center energy of 6.4 keV .
The interstellar column density of \sim 3 \times 10 ^ { 22 } cm ^ { -2 } may indicate that AX J1841.0 - 0536 is located at a tangential point of the Scutum arm at \sim 10 kpc distance .
The coherent pulsations , large flux variability and the spectral shape suggest that AX J1841.0 - 0536 is a Be/X-ray binary pulsar .