The dial of this watch is from the Seiko SNK621, inside is Seiko caliber 7009 a SNXJ precursor automatic watch movement produced from around 1979 until 1996. The actual SNXJ line was discontinued in August 2014. There are some differences of course in that the 7009 has no display caseback and is therefore much flatter.
Inside the stainless steel case of the SNXJ line, you can find the revered Seiko 7S26 movement. This automatic caliber beats at 21,600 bph, uses 21 jewels and has about 40 hours of power reserve. While it isn't the most precise movement (-15 to +25 seconds per day), it is known for its durability. The 7009 on the other hand has 17 jewels and has better quality materials.