To provide shrinkage reducing agents which render excellent shrinkage reducing effect and frost-thaw resistance to cement compositions such as mortar and concrete without entraining excessive air, and exhibit excellent solution stability.
The shrinkage reducing agent comprises a (poly)alkylene compound having an unsaturated bond represented by the formula (1):
R
2
O—R
1
—O-(A
1
O)
n
—R
3
(1)
-(A
2
O)
m
—R
4
(2)
(wherein R
1
is a C
2-10
hydrocarbon group having an unsaturated bond; R
2
is hydrogen or the formula (2); R
3
and R
4
are each independently hydrogen or a C
1-8
alkyl group; A
1
O and A
2
O are one or more kinds of C
2-4
oxyalkylene groups; and n and m are mean addition numbers of moles of A
1
O and A
2
O, respectively, and 1 to 20).