A pyrrolopyridazine compound having the formula (I) or a pharmaceutically acceptable salt thereof:
1
wherein, R
1
is a C
2
-C
6
alkenyl group, a halogeno C
2
-C
6
alkenyl group, a C
3
-C
7
cycloalkyl group which may be optionally substituted or a C
3
-C
7
cycloalkyl- C
1
-C
6
alkyl group which may be optionally substituted. R
2
is a C
1
-C
6
alkyl group. R
3
is a hydroxymethyl group, a C
2
-C
6
aliphatic acyloxymethyl group, a C
6
-C
10
arylcarbonyloxymethyl group which may be optionally substituted, a C
1
-C
6
alkoxycarbonyloxymethyl group, a formyl group, a carboxyl group, a C
1
-C
6
alkoxycarbonyl group or a C
6
-C
10
aryloxycarbonyl group which may be optionally substituted. R
4
is a C
6
-C
10
aryl group which may be optionally substituted. A is an imino group, an oxygen atom or a sulfur atom. These compounds exhibit excellent gastric acid secretory inhibition activity and gastric mucous membrane protection activity etc. They are useful for prevention or treatment of ulcerative diseases and for
Helicobacter pylori
infections.